- Why New Vegas again? We've seen the Mojave already, and it was fantastic, if you're going to re-create another Fallout environment go do FO2's Bay Area so we get a glance at San Francisco post-war, or even better go explore a new environment entirely.
I would definitely be up for re-exploring the areas of Fallout 1/2. They've not been seen in a 3D game yet and are obscure to a lot of the modern Fallout players who aren't so interested in turn-based isometric RPGs.
I don't want to visit New Vegas again because we've already explored it in detail. I don't want to see the exact same towns, factions and vaults.
I don't want to see the setting in the future because NV had so many varied endings that it would be impossible to follow all of them. They would definitely end up making several endings canonical which upsets others who never chose those endings.
I don't want NV in the past either because it would be so limited in story. I don't want to see the return of Mr House nor the First Battle of Hoover Dam as those are events so close to NV that you constantly hear about them. What else is there to explore if we go back earlier to pre-Strip or pre-Caesar? We can't even explore Nellis or the Brotherhood as those interactions in NV were unique.
If we revisit anywhere it should be FO1/2, as at least we would be at least 100 years later if we're set around or after FO4.