The concept of "Main Tank" and "Off Tank" are outdated and not representative of the current and probable future tankIMG mrta. It's better to simply use the term "Tank".

In regards to your question , I don't have beta access, and have zero interest in it, but if the agro mechanics are in anyway similar to WoD, as long as you and your co-tank are decent, agro will be a non issue. At most it will dictate who should pull the boss