I know Bethesda's already greatly improving the dialogue system... you and the person you're talking to can both move around now during dialogue, and they can continue doing tasks, right? It would be cool if they took this one step forward. Imagine if you're walking down a town and someone initiates conversation with you from behind. Then you can choose to turn around or not, and maybe the dialogue would reflect that. Or imagine if your sitting down at a bar and the person next to you starts talking to you while you both face forward. After you two exchange a few words he introduces himself and you can choose to shake hands.
SHAKING HANDS! THE NEXT GREAT FEATURE! Lol, it sounds stupid now that I've written it.
Also, entertainment should be added to Skyrim. Comedians, singers, plays... that would be amazing.