Well, being from Seattle, I'd like to say Seattle would make a great location.
Not only could their be references to the old '62 worlds fair, but due to Washington being the closest mainland state to alaska, maybe that could play into it somehow?
not to mention that to the east of Seattle there are mountains, and some pretty woodsy areas that might make for interesting species (bigfoot anyone?)
Hey! Ghouls could live in the old http://www.tripfilms.com/Travel_Video-v68877-Seattle-Weird_US_Seattle_Underground_City_Tour-Video.html! that would be awesome! ahh man. Now I got my hopes up
Besides, there is little to no history on what happened in Washington during/after the great war. Most of the fallout history is based in CA/NV, and the east coast (DC, Pitt, Commonwealth, etc)
But I say nay to NY as the next fallout, so many games and movies these days are focusing on NY. NY is always either getting blown up, taken over, destroyed, or played in that it's just getting kinda old. I mean, I like NY as much as the next guy, but I am glad Fallout is staying away from the impulse to make a New York based game. I think it's actually cool that they have done Las Vegas and Washington DC. both of which are almost never used for games.
Same thing for Seattle