I really loved the idea, they mentioned in during the EA about having kind of coop arena brawls. You create your characters and get pitched against other players with equally 'low level' characters. After the fight you get your spoils and exp, can level and upgrade gear for the next fight. Though nothing seems to be done into that direction by the end.
I'd like to see a "do arena as you play the storyline*, then, after you're done you can continue levelling up doing arena".
This would be something. Maybe some extra currency for arena gear and similar things, would add a whole new dimension to this game and increase replayability 10x.
* like WoW does it with queueing up for PvP matches