While I admit New York would be awesome, it's not gonna happen. At most, NYC would be a heaping pile of charred and crumbling rubble, while the rest of the state would also be obliterated due to the effects of the bombs.

I would like to see it be in the Great Lakes region. For one, I don't think it was ever explained how that area ended up after the bombs stopped falling. Maybe Chicago, Indianapolis, or Dayton (since there is a well-known Air Force base there) would work? There are plenty of caves in southern Indiana, so maybe Vault-Tec made some vaults there?

It does seem most likely at this point that Fallout 4 will be in Boston. I guess I can always hope for Fallout 5's location. Hehe

I guess we have to think about the developers as well, It would be almost imposible for them to generate places like L.A or San Francisco. I guess they could of picked worse, still I wonder what Detroit would be like in the fallout universe.

Would it even need to change at all?

I have to say London because I grew up in the city as a kid an I would love to see it personified in the fallout universe(got this feeling that the British empire is do for a comeback). But considering the games creators are american and all of the back story and previous games is situated in America, I would say the commonwealth. it's been spoken about and the entire android slavery thing would definitely make for a great story line, being robot Lincoln would be nice wouldn't it.