I think I said this in another thread before but I would return stances back to tanks, just with a different approach.

Make the DPS stances provide a stacking benefit the longer you can stay in the stance (obviously with a cap) and the tank stance provide mitigation benefits.
Then cut down on tanks' mitigation cooldowns so you can't simply 30%+30% or 20%+10%+30% every buster, make tank stances a necessity to survive mechanics at some point.

Then it becomes about deciding when to use your defensive stance to survive and when to use your defensive cooldowns so you can stay in DPS stance.
Enmity doesn't even factor in here, because the most interesting part of old stances were the job mechanics attached to them.