I'm thinking something very similar to what GW2 devs have decided for their game: they removed, in fact, healer class in such way, they have supplied healing capabilities to every job, so every job can put in hotbar healing skill and be the healer of the group.
In this game I would remove the tank class, giving DPS and TANK abilities to all melee classes (war,monk,drg,pld) or even to whole actual classes. In such way, the queue problem will be solved.