I don't know much about programming, so, how hard actually was it for Bethesda to put out the free upgrade for skyrim to 64bit? Crusader Kings is also doing the same thing. If it's not that hard, poo poo on Obsidian for leaving the game with a broken mod limit. It'd make a great "thank you" for their dedicated fans. I could picture CDProjeckt doing that.
But then, maybe it's really hard and no wonder they didn't do it.

Someone I know told me that a programmer almost got the FNV launcher 64bit enabled but got a cease and desist from Bethesda's lawyers before releasing it.

Possible yes, gonna happen? Sadly not I think

Yeah, I know it's not going to happen, I'm just trying to decide whether or not it's understandable or crappy that Obsidian left it in its current state, with a broken mod limit. Yeah, I know, I'll hear from a lot of people are really surly because the mod limit didn't affect them, but it did for me. Yes, I've heard of merges.
So is it just flipping a switch and they were lazy and just said hell with it let's not bother with fixing this?" (I'd very much expect that from Bethesda if they'd done New Vegas.
Or is it a multi-million dollar endeavor? Maybe Bethesda shut the door legally and prevented any further fixes or 64 bit updates from Obsidian? I have no clue at all.
Some developers provide support, free content, and patches for a game long after it was released.

From what I understand is the application would have to be completely rebuilt to run as 64bit.

I know nothing about the process but I do know it's not something that is casually done, more so it's going to be near impossible without the source code (I think..)

Here's a post I found that might help: https://www.quora.com/How-do-I-convert-a-32-bit-software-into-a-64-bit

I'm (pretty sure) Obsidian has the source code, they're the ones I'm talking about. I'm not expecting a modder to be able to do it. There are a fair number of people wanting a remaster, and even just a bug fix and a 64-bit upgrade would be welcome to that crowd I'd think. I got the 64 bit upgrade to Skyrim for free, and that's from Bethesda, who are truly infamous for sloppy, lazy, greedy work. If Bethesda can put out an upgrade for free, anyone can. Well, I'd hope.
Honestly I think a genuine upgrade to New Vegas (so long as they didn't downgrade features -- just modernize and fix) would fly off the figurative shelves, probably sell better than the original somehow.