hard to speculate without knowing the full particulars of what the court ruling was, (ie: did bethesda forbid gamesas from using what it might consider it's property in dc and vegas? (though legally that would be impossible for bethsoft to claim since beth could only protect it's concepts and ideas, but not the actual regions....but that's for lawyers to haggle over not me
)or is gamesas free to use any regions as fair game. if so i'd see chunks of states perhaps. as other have stated maybe parts of the east coast, or the west? groups of 3-5 states with players having the choice of starting areas/states based on preference, faction or other similar mechanics implemeted in the game.
definitely would add some variety as each region would be a little different as far as unique critters/monsters while having similar cross-over species from region to region. that's nothing new as most games do it that way, just stating as an example. being unfamiliar with fo1 or 2(my fo baptsim was fo3 and expacks thereof)i'm not sure how viable the regions covered in them would be but there you go. what that would essentially do is spread the player population about to avoid some overcrowding.
i'm with deathclaw dave, i love the exploration as long as there's the ability to escape from things that are out of your league(or rather the other way around) so the bigger the better. don't want to accidentally blunder into something that will eat me in 1 gulp. hurt me to within an inch of my life as i deserve if i wasn't taking precautions, but that's all.(i tend not to die since i'm VERY cautious while exploring). long winded enough i'd say so i'll stop at that.