Just a thought, but if there was a nuclear winter to occur in a future Fallout game, wouldn't it have to be set fairly far in the future, as the world in Fallout 2 was quite the opposite?
I understand that after a nuclear blast, the fallout and whatnot heats the earth, then cools it, heats and cools blah blah blah... And with each repetition, the cycle becomes shorter and shorter, till eventually the fluctuations become minor.
Which brings upon the debate of the time that Fallout 3 will be set, according to the date of Fallout 1/2.
If the game was set too far into the future, the technology may have changed, and hence society, thus leaving a gap where the player does not understand what has happened since the last Fallout, depending on whether the game IS based on the previous Fallouts.
Anywho, the nuclear winter may be a different approach to the Fallout genre, but definetly would not fit in.