London would be pretty weird. Come on, how those brits drive their cars! They have totally different roads, and you cannot deny that if you make game using that country. I don't think it would be interesting for people to play something like that. And why would they move to Europe? Personally I think that it would be pretty fail. Everything and always on what GTA is based happened in America and only. I think that before moving to Europe they would make something with Mexico or so at first.