An actual Undo cooldown would be great to have to be honest. Set it once on a target to memorize their HP and put a buff on them. Hit it again to set their target's HP to that value. Limit it by the buff's duration (10-15s), and give it a large cooldown. It would be their equivalent of Benediction but be a little slower. Only WAR would really break it and that could be accounted for.

The only reason I don't want it that badly is Essential Dignity is already really good and AST needs their issues resolved first, not more tools that infringe on WHM's few remaining niches.