Well, seeing how the war was between China and America I'm going to rule out Europe. I find it difficult to believe that the continent could get away from such a huge global crisis, but even still, it wasn't exactly central figure of all this.
Before the war sounds... Like a normal boring life. Like all the cutesy pre-war advertisements in the game. In which case... It isn't Fallout any more, is it?. You know what the title "Fallout" refers to right? Nuclear fallout. As may be observed in the event of nuclear fission.
China, while being the other key figure to the Fallout back story may seem like an interesting choice, but consider as fact that a good amount of the atmosphere of Fallout can be attributed to sprawling wastelands interspersed with surviving locals attempting to make do with a bad situation. There's a real sense to it all that suggests that humanity has the strength to live on, even in the worst of times. I'm not suggesting that this wouldn't be the case with surviving factions of humanity in China, but the fact is that I don't speak Chinese and having mainland Chinese people speak anything other than Chinese would seem like a dumb idea. Sure, you could play from the perspective of an American in China, but it beats the hell out of me how you could create a story without having the ability to communicate. Sounds kind of dull to me.
Any other country sounds pretty unappealing to me from a story wise perspective.... Although I admit, you could get some pretty awesome mutated animals in a Fallout Africa or Fallout Australia. Like a mutated hippopotamus or a mutated kangaroo. Imagine that... You're running along fighting Radscorpions or whatever and this Radaroo bounces out of nowhere and embeds your jawbone into a rock with a single kick. That would be cool.
I wouldn't vote for cancelling the series, because I have enjoyed the previous games. I would however like to see it evolve into something. Fallout 1 and Fallout 2 were fairly similar in gameplay using the overhead, side scroll, "Diablo-esque" method of gameplay. The jump between Fallout 2 and Fallout 3 was huge, going from Diablo to a split First/Third person game. Fallout 3 and New Vegas were essentially the same game. There were some new enemies, different skills, weapons etc. but just about every significant gameplay mechanic was identical to Fallout 3. It wasn't really a problem because Fallout 3 was a pretty good game regardless, but I would like to see a new Fallout game do something new that I haven't seen before.
As an Australian who hasn't travelled I don't know much about America so I can't really suggest anywhere with much justification. New York sounds appealing but I think it is probably too big of a city to really be in a Fallout game. A lot of the pleasing visual aesthetic of Fallout is attributable to the sprawling wastelands.
Then again, New York could be part rainforest for all I know.
I trust that Bethesda will make a good decision, when and if they return to the series. Which of course, they will, because New Vegas hardly killed the series, so a sequel would be a guaranteed profit turner.
