Like it or not, the Bethesda model isn't going to change much. I like the original Fallouts, but I also like Elder Scrolls, so having a post-apocalyptic one is cool with me.
What I would like is an even more hardcore mode. I want you to need to sleep every day, to need to drink lots of water, to need to eat every day, or suffer serious consequences. That seems doable.
I'd also like to have more opportunities to be "evil" than New Vegas (they didn't even have any evil companions!)
Something I want (but probably won't happen) is destructible surroundings/buildings. Can't pick the lock? Blow open the door with dynamite or knock down the wall with a super-sledgehammer.
Also, get rid of or seriously reduce fast travel. Maybe introduce vehicles to offset the traveling time or only make fast travel possible only between certain places (like the silt striders or mage guilds in Morrowind). Also, add more random encounters. Maybe bandits stop you on your way to a certain area or something like that.
More puzzles and problem solving.
Get rid of the goddamn compass for quests and give hints so we have to figure out where to go, don't just tell us "Go this way."
Most of these seem reasonable and doable, but I doubt they'll be implemented.