Please keep tanks out of arena brackets. It is incredibly unfun for the majority of the playerbase. To throw out a buzzword the gameplay is "toxic".
So, here's the thought process: Yes, fighting *against* tanks is not fun right now, on live.
On live, our solution has been "Tanks, stay out of PvP, for the most part." That's fine for the non-tanks; they don't end up having unfun fights against tanks. However, for the tanks, it's really disappointing.
In Warlords, we want to try to find a solution that keeps it fun for the non-tanks, and lets tanks PvP. Tanks no longer have massively more CC than the DPS. They're already going to be tuned to do somewhat less damage than the DPS, with Vengeance removed. The remaining thing that's unfun about them is how invincible they are; we want to try to solve that.
Feedback from players is going to be instrumental in this process, and we're going to have to iterate on the solution, I expect. There are going to be some players who just see a tank in PvP and have an immediate gut reaction of "ew, go away"; that's not the feedback we're going to be looking for. We're going to be looking for the feedback from people who give it a real try, and share "OK, this is the problem, this is the part I find aggravating, here's the issue with how they fit into the metagame, etc."
TL;DR: We want to make tanks fun to play and fight against
in PvP, and we're going to need your help to reach that goal.