I've said as much before but I think it bears repeating. Much of what makes Fallout what it is, is the twisted version of Americana that we get to explore. The feeling of nostalgia combined with WFT.
Much of the charm of the games is this trek through a pastiche of America, not as it is, but a skewed parody of an ideal. If you were to move it somewhere else you may get a good game, but not a Fallout game.
Fallout works, for me at least, because it's so tantalizingly close to true Americana, but somewhere it all went horribly wrong and now we're left with a nightmare distortion.
As I said, an important aspect of all the Fallout games has been the recognition of our own society gone insane and a kind of melancholy. If the game was moved to, say, China, I would not know the society and not know how it had changed. It would be great for the Chinese players I guess, but for me it would be weird. I would lack the frame of reference I normally have in Fallout.
That's not to say I wont play a game set in China (post apocalyptic or not) but I'd rather play something new and not a Fallout game. Fallout is a take on the US and western way of life. Leave the rest to other games I think.
Edit, because I'm grumpy today:
It would be like moving Max Payne to Brazil or X-Com to the 50's. It would defeat the point of the games and take away what made them unique. Oh, wait...