Since you cannot build aggro in pvp in the traditional sense, wouldn't it make more sense to not have a specific "tank" role for pvp? This would also improve pvp queue times as a Paladin or Warrior could queue as a dps and any of 7 classes could fill those 3 spots rather than requiring one of 2 specific classes to fill one spot and leaving the other 5 classes to fight over 2 spots.