I personally don't want it to be set in a big city again i liked the open feel of new Vegas alot better then i did in DC, DC was just to "cramped" for my liking and got really sick and tired of moving from subway station to the next... wasn't much diversity in the scenery...
Don't blame the setting, blame Bethesda.
There's been a few discussion threads I've seen that have discussed where FO4 should be, and I have to say South Florida would make a great location.
>actual weather
>canals and rivers everywhere
>Biscayne Bay and the islands ringing it in general
>the last two may lead to the creation of usable boats
>new mutants from the sea
>DLC goes to the Everglades and Disney World