I’d be pretty happy with some minor features I don’t think an MMO can go without theses days:
- Inspection option
- Player to player trading [no mail or trading post involved]
- Mail that requires a payment to open, similar to trading
- Alerts when people in your contacts list come online
Then come the bigger features:
- Player instances including full-fledged homes
- Guild halls for each guild, for a fee
- Guild vs Guild battles