Mini Games like setting up and defending a fort. Easily included in the Civil War quest line.
Fatigue/exhaustion effect if you do not sleep. A bit like Vampire effect if you don't feed, but negatives on your attributes/skills. Cured right away after 8h of sleep.
Decoration for houses with like trophies and stuff. That will make each house more personified.
In addition to spear/lance, as they now have mounted combat, a knight championship would be nice, with event like Sword Fighting, Joust, Archery etc... Player can get glory in each city for tournament won as well as title of Knight Champion of Skyrim if he wins the Championship. (I know, I'm a fan of "a Knight Tale" movie
)
Flirting Mini game. I feel like the way you can marry is lame. taking out all the fun of the game of flirtation.