Priest had always been a great healer option. Holy priest got several AE heal. And then disc priest got shield and atonement which mitigates a great deal of maintenance in a 5-man team. The sad thing is they got nerfed and the DPS was just too bad yet the healing wasn't too good neither.

But as mentioned, atonement receives a drastic change in legion as atonement becomes somewhat flexible and it can heal more than one target. The pre-buff requirement shouldn't be too bad thanks to isboxer.

But then the most important problem(?) is legion requires a LOT of tank healing it seems. So it may not be much viable to bring one single healer. Comeback for support healer, perhaps? I'm already thinking bring a disc priest to fill the support role. The constant, managed healing should help ease some attention from us looking at the health bars all the time while not sacrificing DPS too much.