I personally would like to see less of a focus on technology. In the first two Fallout games there was some high tech, but it wasn't in your face. Most people were eeking out an existence on a very simple level...many were even primitive tribals. It wasn't until later in the games that you would see more and more of the really high tech outside of what you see toward the beginning of the games in the vaults... You'd go through the first half of the game with everybody fighting with spears, knives, simple firearms, etc. Then later in the game when you see your first supermutants and BOS and somebody breaks out a minigun or an energy weapon you're like, "HOLY CRAP, WHAT THE HELL WAS THAT!?!?!"
That's kind of my thoughts as well. I think Fallout 2 did an especially good job with the technology. Starting out with just things like spears and such was a nice change of pace, and it made finding those higher-tech items seem that much more valuable. They also did a real nice job with the pacing in that game, where you actually spend some time with the lower-value items before moving onto the big guns (you could of course jump right to where the good stuff is if you know where you're going, or run into stuff at random, but they also did a good job with pushing you in certain directions throughout the game so the progression felt real natural.) I still remember having to save up to afford even one stimpak, or a pistol, and thinking Combat Armor was just totally out of reach for a long while.
Personally, I think we're pushing it a bit with the game now taking place 200 years after the War. I think at some point if we keep making jumps like that, we'll be seeing more of a rebuilding effort going on in earnest. Not that's a bad thing, just getting away from some of the really neat things about the previous games. I can sort of see it making sense that all this stuff is scattered much more liberally around the DC area, as it's a smaller area in scale and also the source of a lot of good Pre-War tech and such. I'd go as far to say that maybe a next game could be something of a flashback of sorts, taking place in a time parallel to the adventures in the first two games, only in a different area. That would make the harshness seem a bit more believable, at least to me.
But I do think it works best when you start out with a much steeper curve in obaining items. When you start the game with nothing and have to scrabble to even find so much as a working pistol for a good portion of the game, it just makes it feel that much cooler when you're finally strutting around in Power Armor with your trusty Plasma Rifle.
Anyway, back to the OP, Seattle might be an interesting idea. I suppose as much as any other part of the US, really. Something tells me we'll be sticking to the East Coast for a time, though. Looks to me like it'll be moving North a bit, into the New England area to deal with the Commonwealth and such. (Which is likely going to introduce some higher tech aspects as well, come to think of it.) Personally, I think we've done the whole "Vault Dweller" plotline enough that maybe the next game puts you back as a Tribal, if for no other reason than to start you at the bottom of the tech chain. I just think that would be more fun to play.
There's also a lot of stock for some interesting stories between the Coasts, as well. There's likely a whole epic storyline just dying to be told of Lyons' detachment making the trek from California to DC, for example. So I'd like to see something dealing with that as well. Maybe in a very large DLC or something. Or even sort of an episofic DLC would be a better fit for the scale of something like that. Plus, the Midwest and a lot of the smaller towns may not have been hit as badly during the War as the other areas we've already explored. It could be a completely different situation there, really, with the area more intact and some actual foliage and such, trees and whatnot. But instead of dealing with radiation you're dealing with the breakdown of the infrastructure holding the country together and more solidified settlements fighting off roving bands of raiders.