Something that is missing in my opinion is the follower system, companion if you will, not to help player level or avoid completely the grouping, but to make NPCs interactions more useful and to feel more like an active world.
My idea is giving the option of recruiting some NPCs to become your follower, not with powerful attacks, only slight support spells or attacks that will help the player a little bit. Followers may help the player with inventory space, maybe 10 or 5 extra spaces.
And that's my idea of a follower system, just to make NPCs more important to players and increase the immersion in the game.