Collision detection and tank gameplay
Tanks on PvP are just DPSes with a few twists right now; it is sad to see so much wasted potential on a role that is essential everywhere else.
Anyone who played PvP on MMOs that had collision detection knows this: it's a game changer. Tanks can form shield walls and hold off enemies, while healers keep them alive and DPSes cause heavy damage on anyone on the other side of those shields. Choke points (like bridges, staircases, gateways) create a whole new level of strategy that we just don't have over here.
I've been reading that we are getting some kind of PvP overhaul on 3.2 and think that this would be a nice thing to add. Please look into it SE.