If they wanted to give tanks a dimension like this while still trying to keep Enmity out of the game (without having to put forth the cost to code it out; obviously its still there), they could simply:

Increase Provoke Enmity generation obscenely again, so tanks can be ahead of each other on Enmity.

Add 'generates additional Enmity ' to all tank actions, just to preserve that post 5.0 'make sure they're ahead of non tanks' Enmity flavor.

Drop Shirk to 30 sec so tanks can still do the older fights that require swaps more often than once every two minutes.

GNB's PVP incarnation already provides them 3 stances, and the same could be done in PvE with a Draw and Junction, using available players and themselves like BLU mimicry.