Equipment maintenance to come back. Presto, another way to help level smithing without grinding if you like.
More incentive to use Food/Cooking - be that survival requirements or better bonuses from cooking. have never used it because it seems worthless and extra weight to me.
more effort on the part of a more indepth environment. "Filler" NPC's with only one topic to discuss and only 1 line of dialogue may as well not even be there. lets have more factions, and dispositions you have to work at to maintain/improve. Make speechcraft have a purpose other than buy/sell/very rare persuasion check.
Keep the house building - but don't turn it into a pay for it DLC. Hearthfire was a bit cheeky IMO, perhaps not as bad as oblivions horse armour but it should have been included in the base game.
Better horse combat. Give me a reason to want to use horses. make them faster and more nimble, skyrims horses seem like driving a four legged forklift.
Magic Damage to be balanced out a bit more to keep it effective at higher levels.
Mai'q.