Oh, dear god. Do you know what you've done? RPers like myself are about to give lists that will make the devs start drinking more heavily than they already undoubtedly do. That said, I have no guilty feelings.
1. An extensive emote list, complete with animations
2. Enough gear and costumes to make the "clone effect" something that will have to be actively done by players
3. A music system at least as good as LotRO's, if it can't be improved upon
4. Guild housing, if not player housing
5. Player created quests (rewards for completion not necessary, but welcome. Obviously, this will need to be monitored)
6. Different styles of dancing (this could be part of number 1 above, though)
7. Player-run shops
8. A system similar to WoW Modelviewer and Movieviewer
9. Emotes that are interactive with other characters
That's all for now. Obviously, some are more likely to happen than others, especially in the short term. I reserve the right to add to my list as I think of them.
EDIT: The additions, some of which are reminders from other posters
10. Dueling
11. Mini-games, especially within taverns
12. Mini-pets that do more than just follow you around
13. An M-rating (okay, not strictly an RP element, but I'm bloody tired of the T-rated games and their stories. I don't want pixelated boobs, but a story that doesn't rely on poop jokes and pop-culture satire would be nice)
14. A story that makes sense, and doesn't rely on NPCs being total morons
15. Unarmed combat