Midwest US, Hawaii, Alaska, Europe or China, there is still a lot of good real estate in the fallout universe that can be explored. I'm thinking the next game will be set in toronto tho, as fallout 3 heavily hinted at the region without explicitly saying anything about it, same as with vault 76 in one of the terminals in the citadel

Honestly, tho, I would just settle for a 3D remake of tactics or van buren, those had really good worlds

Bethesda traditionally sticks to the East Coast, so New York would be very interesting to see. However I doubt that they could pull it off because of technical issues (i.e. downtown Boston...)

I would love to see Canada, just for the post-annexation lore, same with Mexico.

However realistically I think they might choose Florida - Bethesda likes swamps for some reason (Point Lookout, Far Harbor was swampy too).

I always wanted a New York city fallout but according to lore it was destroyed by multiple nukes. Other then that a fallout in Japan would be interesting to me.