Hopefully some robust RP tools... if at some point they can implement anything remotely like the LOTRO music system would be amazing.
Robust crafting... make crafting worthwhile for everyone, if even the guys who are maxed out can find something useful from crafting that will help stop everyone from being too independent. Both AO and EVE had very robust player driven crafting that IMO went a long, LONG way towards their success.
Open world events... few things pull a community together like having stuff take place out in the world.