What does active mitigation seem to be for prot warriors?
It must be a new concept for the rotation does it not?
It can't be the use of long cooldowns (shield wall, last stand) that we already have and it can't be the use of short cooldowns (shield block, shield barrier).
What seems to be changed at this point is only the rage mechanics and those are the similar for all warrior specs, be it dps or tank.
Conclusion should be that the active mitigation model that was spoken about when threat got obsolete is for warriors not yet implemented?