From what I understand, if they removed cleric and allowed full dps any time, it would wreck the pvp balance they have by not allowing cleric dps. Granted, they could fix that by putting an 80% dps down debuff on healers but that is one of their reasons. If they were to remove cleric, it would be in 5.0 as they would have to rework a lot of content around it. The other issue about removing cleric is that the demands for people to dps all the time would skyrocket.