The next fallout should not go forward in time. I think F:NV is great, the best game of the series IMO. But, but... we're going too far into the future. F:NV is really pushing the line between post-nuclear america and some 3rd world country simulation.
I say Fallout 4 (or whatever) needs to go BACK in time to sometime within 50 years after 2077. It could be anywhere, just don't go forward in time anymore. We're starting to lose the "Fallout feel". I DO NOT think we've lost it, just that we will if the series continues to go forward in time.
That is all.