Arguably tanks should have no place in PvP. Their function is to mitigate aggro, and the only aggro present in PvP comes from pets.
I am sorry but this is completely wrong, a tanks function is to mitigate the damage a group takes not aggro. Aggro is simply a mechanic to help mitigate a groups damage by having the enemy focus on 1 player (who takes less damage than others) instead of many.
This function can carry over into PvP if done correctly, and it looks like TOR is doing just that. Tanks will be able to fulfill their role in PvP by helping mitigate enemy damage through the guard and taunt mechanics.