Probably been said before but it helps to emphasize it, ESO needs:
_ Duels!
_ PVP outside Cyrodiil. It was revelead early on there would be matching options to gather the people of same tastes( pvp, pve , RP ). ESO would be a much better game with this option, spontaneous PVP while leveling, public dungeons wouldn't be a faceroll but a much more dangerous place instead.
One thing that it doesn't need but would be appreciated is Arenas or some sort of battleground for some quick PVP. Instead of always having to depend on your friends to be online to make proper pvp in Cyrodiil or just follow the zerg train which gets old fast, instanced pvp would be a nice alternative for the down times.
How these features are not implemented in a MMO launching in 2014 is beyond me but doesn't hurt to give you some feedback.