And IMHO this is FO3's best feature. It makes it seem more real, and makes your jaw drop.

Lets face it, FO1/2 could have been anywhere. There was little, if anything to make you think the boneyard was really LA, or San Fran was really, well, San Fran.

Riiight, your jaw dropping because you see the husk of the Capitol or the Lincoln monument ? Neat window dressing I guess. And you only see bits of LA and San Francisco in the earlier games (and I'd think most of the monuments would have been dust or total ruins at that point).

Like others have been saying - I'd have trouble seeing a setting other than America as properly fitting into the main series. There's a sort of nostalgic Americana at work in the Fallout aesthetic, and Fallout 3 is really just Bethesda's first go at this. It seems a bit early to start mucking around with a change in scenery too much, until the new series is more well-established. (ie, as a nice change from "yet another Fallout set in America," a move to Europe might be interesting, but I don't think we're at that point, yet. Especially as Bethesda is really just starting out with establishing the game for a newer market.)

I could see a spin-off of some sort taking place in other locales, though. I know, I know... there's plenty of sentiment around here that thinks "what's the big deal with proper naming?" But I think that I, personally, could more easily play a Fallout game in Europe or another country if it was billed as "Fallout: Across the Toxic Pond" or whatever, and released in conjunction with a more "traditional" Fallout 4 still being set in America.

It would seem to me that any Fallout game, even if it were otherwise the exact same game as Fallout 3 in terms of gameplay mechanics and ruleset, that took place in another country would bring in totally new factions, monsters, storylines, etc. There's no in-game fiction (that I'm aware of) pointing to Fallout-centric elements like Vault-Tec, Supermutants, the Brotherhood, Enclave, etc existing anywhere other than America. They might have their own anologues (ie, I'd imagine England would have shelters of some sort, and you could possibly start the game out exiting a bunker; there might possibly be some factions that are functionally similar in mission statement to the Brotherhood, Enclave, etc,) but it would almost seem like a cop-out if the game was set in another country and had all the same factions and enemies but with different names.

I think the differences would serve to make it a completely separate story arc from anything taking place in the Fallout main series, so I personally think it might be a poor fit for a Fallout 4 as opposed to a spin-off.

That said, it could be an interesting spin-off exploring what's going on over in England. England's experience during WW2 was quite a bit different than what he had going on here in the States, so I think there could be an interesting twist on the aesthetics of the retro-futuristic feel, dealing with a different cultural history. (For example, it seems like there'd be a clear anology between the War of 2077, and the bombings of London during WW2, in regards to that setting.)