So, in this imaginary sequel, the BOS, NCR, and Enclave, and maybe even the ever-present usual suspects like Deathclaws and Radscorpions, will not be present.  Stealth suits will no doubt be available, as well as a remnant of the American pre-war invaders.  There will probably be Chinese factions of all sort. We can probably skip the super-mutants too, as I really think they too have been over-used, unless there's already definite lore reference to FEV super-mutants in China.
But what completely new things might we see over in post war China?
I confess that I'd really love to see some playable races other than "human." Something we haven't seen yet, a result of some kind of mutation, cybernetics, robotic, or genetic splicing. Playable non-human, post-human, or barely human races are something we haven't, surprisingly, seen in fallout yet.

It would be very cool to see all the Chinese aircraft, uniforms, and weapons everywhere. It would also be cool to see how the propaganda in China was before the great war. Looking at all this equipment, as well as the Chinese submarine seen in Fallout 4 concept art, I think that China may have looked somewhat cyberpunk before the war. I wonder how much bombs were unleashed on China from the U.S. though and if there's anything there. It is possible that most of China could look like the glowing sea considering that it would be the united states main focus. The idea with more races is great and I'd love to see that too in a future game.

A decision would have to be made on culture and technology as well. Was the rest of the world stunted in some kind of weird futuristic-retro combo? Maybe it was the US who was strapping lasers to 1960's tanks, and China was using something more like 1980's or 90's technology (other than things like the stealth suit.) I don't think we know from the lore alone with certainty and detail.

I'd love to see something like this. Unfortunately Bethesda'll probably never do something like that as they depend on the established iconography to sell Fallout.

If relying on past lore is absolutely necessary for Bethesda to do anything with Fallout ... then perhaps a BOS or Enclave expedition to China. They've got reason to want to get the heck out of NCR territory. I could take place shortly after Fallout 2, as it won't rely on or connect to anything that happened in the other more recent games.
That way old Fallout veterans would exploring something very new, while also having some connection to familiar things.

I don't know if I'd like to see a Fallout game set outside the United States honestly. Without the setting, characters, factions that all Fallout games have had in common, would a new title stripped away of most of that really be a Fallout game? I believe that the setting of the retro-futuristic United States is essential to the setting of the series as it's what made it unique in so many ways. As @Sirdanest said, I don't think I would mind a Chinese/Foreign setting if it somehow managed to incorporate existing elements of the established game such as factions or characters. A spin-off title or DLC into another country would be the best bet, but I don't making a hypothetical entry into the series a numbered sequel would be a good idea.

Also, lore-wise, didn't Mothership Zeta in Fallout 3 (as bad as it was) establish that China was nuked to hell in the Great War? I've heard theories that the "Great Beyond" that the Ghouls in NV wanted to go to was the irradiated crater that was post-WWIII China.

@"thegreataimbottio" I can see the wisdom in concern over how difficult it would be to establish a location like communist China in a game like Fallout (at least, current-gen Fallout).

A lot of the tones from the 3D games are set with hyperbolic, patriotic American themes.
Though, it would make for outstanding RPG fuel if we, the player, experienced being tossed in a foreign land and being exposed to new information along with the player character. How this situation would happen in the first place would require some decent effort in writing and storytelling, though. Maybe a plot device using a restored Chinese Submarine, like in Fallout 4.

That sounds a bit unrealistic, though. But something along those lines sounds about right.

If it was set in China, i could imagine something like whatever is left of the American army, has turned into a large mercenary band, selling their services with their high tech Power Armor, to whoever is willing to pay in the post apocalyptic society.

But I dont think a China setting is very good. The main visual appeal of Fallout is it's 50s American themes and style. All of that goes away in China.

It'd be nice if there was a DLC set in China, or a mission or two. But not a whole game.

Yeah, maybe I shouldn't have said fallout 5. Maybe a DLC for Fallout 5, or something like that. It's possible, I suppose, that the faction remnants of the US invaders could have a base or shanty-town that preserved that part of retro-American culture. There are ways to fit it in. I'm just... I don't know, I like all the tropes we see in Fallout, but, the 3000 miles east to west of the US have things that are so monolith, so ever-present... The Enclave, the BOS, deathclaws and rad scorpions and super mutants and bottlecaps -- I'd once upon a time thought all those things were relatively local. But it turns out that they're "everywhere." Back in Fallout 2 days, I'd been dreaming of seeing "how different" the east coast would be. What new factions? What new monsters and mutants? What would they be using as money?
Oh well. So, now I hold out hope that another country will have the things I wished for back then. But then I remember it's Bethesda and if we go to China we'll find that the Enclave, BOS, bottlecaps as the primary currency, deathclaws, and mutated pet Emperor scorpions are also in China. Somehow.

I would love so much to see chinese architecture and really crowded city streets in Fallout. I doubt we'll get it but I love the idea

From what I understand, China is likely one giant crater that's 1,000 times worse than the Glowing Sea. We got a few of China's nukes while they got most of ours and that's a lot of nukes. Now, looking at the glowing sea, only the fiercest creatures live there and not usually in huge quantities, so that means that there isn't much prey for said creatures to survive off of. The deeper you go to the center, the less and less life you'd find and the less and less ruins you'd find. You'd probably only find stuff on the outskirts of the country. I doubt they'll make a game on it.

Also, Fallout is supposed to be about post-apocalyptic American life. I doubt they'll branch into other countries.

I've said it before and I'll say it again. A spin-off game that revolves around the Chinese ghoul in the Yangtze in FO4 once he reaches China could be cool. Highly doubt that it would happen because as @DonEsteban said,the main surrounding theme of Fallout is people surviving in the wasteland of America,living through the harsh environments colored by the remnants of post-WW2 Americana and happy suburban life. However,in a theoretical alternate dimension where Bethesda were willing to go all the way and even think about developing it,I see it as being just a small spin-off game to play in between main releases. Something like Elder Scrolls Adventures: Redguard. Maybe not as linear as I hear that game was,but it definitely wouldn't be as expansive as a main title release. It would probably also focus way more on the settlement building as the ghoul did say that he wanted to go back home and to rebuild if I remember correctly.

A game about Chinese fallout would neither succeed, not be fun to anyone except Chinese.

Fallout is about seeing the society change in the fallout (heh) of a Nuclear war. Seeing how old ideologies change and shift, how the world mirrors the old world and where it does not.

Chine of today is a culture very few are familiar with, and we are in no position to appreciate the transformations the cultures and ethos's would have undergone.

It would either be an big stereotyped joke, or something nigh-incomprehensible.

Besides, China is much more fun as a mystery.

I think it could work with a setting like the survivors of the US occupation force has created a little kingdom from the foothold that they were able to get during the war but they could not push out because the nukes killed their reinforcements and supply nor could they be defeated because of their Power Armor.

It is also essential that the Chinese government is destroyed to ensure that multiple factions from the China will be created. I could see metro like groups forming up like Desert Ranger-like groups banding up from former Hei Gui units trying to help everybody to survive the Chinese wasteland, fanatics from former Chinese patriots, Chinese royalists creating their imaginary Emperor, capitalists from Hongkong, etc. Otherwise it will look like a this guy vs that guy kind of game.

There are also a ton of possibilities in terms of mutated wildlife(Pandas, Alligators, Turtles, Salamanders, Pangolins, Monkeys and a ton more).

I wonder what kind of stories will be told from that kind of world.

I must be Chinese, because I'd love it.
I also like learning about other cultures -- in fact that could actually be part of the game, the recognizable, familiar expeditionary group to China would be strangers in a strange land, making contact with the remnants of the American invaders' underground bunker/base/etc. It'd be the same when going to another planet (another spinoff.) Those two elements would provide a tie to American culture.
As for nuclear radiation, ghouls, supermutants and children of the Atom can all live in the glowing sea. Fallout is capable of being pretty creative (or silly) and "radiation" is absolutely no absolute obstacle.
The Shi were Chinese and they developed a vine that clears radiation... it could have been that they merely finished a project already in existence, since they were naval soldiers and not an actual scientific group. I find it hard to believe, as big as China is, that nothing and no one was prepared for nuclear annihilation. A group of survivalists or scientists could have had an underground base, and build the anti-rad vine.
And most of all, a new species of playable mutation or something. That's the primary reason I'm hungering to go to another country, because I think Bethesda has made the US too monolithically alike from coast to coast, same factions, (mostly) the same monsters, and ugh, the same currency absolutely everywhere even in places with no contact with each other. Why does the institute trade in freakin' bottlecaps, a currency that they are basically trying to destroy?
In the old fallouts, the brotherhood, being isolationists, used their own currency. So did Redding. Black Isle had plans for a far more complex economy. I miss that. But, yeah, Bethesda would probably just have the Chinese using jet and bottlecaps just like everywhere else, nullifying my whole point of wanting to do this.

I'd love to see a Fallout China, but not as Fallout 5. Maybe as the Fallout in between 4 and 5, or between 5 and 6. Honestly, I am worried that if they do this though, it will just be the same stuff we see in the US....Molerats....deathclaws (somehow) Jet, bottlecaps...It is almost TOO different to make it a good game while keeping it "fallout enough" for the normies. Though, that is just my thought.

Yeah, I think there's plenty more to explore in America, but that doesn't mean it wouldn't be really cool to see other places, especially China

There _should_ be plenty more to see in America.  But I'm really worried that Bethesda has just decided that most of America is basically samey-samey.  All barren wasteland, BOS and supermutants are everywhere no matter what, bottlecaps as currency are everywhere no matter what, and certain monsters that should have probably been a more local phenomenon are instead archetypal, iconic creatures found everywhere.  
Meanwhile, logical innovations like player races, visible cybernetics, other types of sentient mutants/gene-splicings are being ignored in favor of re-using things we've seen before in other parts of the country.  The iconic things are everywhere, across America.  So I worry that there is not as much to see as there should be.

Edit: Ok, so imagine this unlikely scenario, in place of Fallout 5:China -- Bethesda tells Obsidian "Hey, you can do another fallout, and take your time if you need it. But, it can't take place on the west coast of the U.S. or Mojave."

Could Obsidian do it? Shortly after the destruction of the Oil Rig in Fallout 2, a portion of the Enclave that wasn't on base escapes to China, seeking to re-unite with a suspected remnant of the U.S.

The invaders of China, who (according to the last known records.) captured an underground Chinese bunker just before the bombs fell.
Maybe the bunker remnant uses cybernetics and have vastly pro-longed their lives and made themselves more hardy in this inhospitable world.

Maybe the player is a maybe-disillusioned member of the defeated Enclave, or U.S. remnant in the bunker.
That's two semi-recognizable American factions.

Meanwhile, scientists in China engineered their own version of the Shi vine and are living in the ruins, cleared of radiation, of some major city. They'd probably have a computer like the Shi Emperor that could make predictions about the future, but maybe it's secretly gone a little rogue and has an agenda of its own that only a few suspect.

Then there's some new species of sentient mutant (I won't deal with the details yet,but there's so much potential) who are another faction,the enclave will no doubt despise them. Honestly fallout has so much untapped potential here to add in a new race that we haven't seen yet.

I bet Obsidian could genuinely make it work.

Obsidian could definitely make it work, but Bethesda has more or less said recently that they will not have an outside company do another Fallout...so I think New Vegas may have been a one off, unfortunately

A really intrepid modding team like that of New California or Frontier might be able to do something awesome there.