Every tank should have a raid CD to some extent or bring something that benefits the raid. Monks have avert harm and guard. Warriors have banners and rallying cry. Paladins have devotion aura and hand spells. Druids and DKs really don't have anything beneficial at all. AMZ really isn't that great and blood worms are just over healing machines. Druids have tranquility but it's only really good with HoTW popped and in a lot of scenarios it's very impractical to cast.
Buffing tank utility really doesn't imbalance the game either because you only bring upwards of two tanks (rarely three) to any encounter anyway. Nobody is ever going to stack tanks. Making tranquility easier to use for guardian druids, giving them another minor raid CD would go a long way. Buffing AMZ for blood, making vampiric blood raid wide and/or giving DKs a bit more control of blood worms (or making them smarter) would help as well.
They also need to look at tanking stats in general. Prot Paladins gear mostly like a Ret Paladin and Monks/Druids actual get benefits from critical strike as far as raiding goes. Haste is still a good stat for Blood DKs but DPS stats are far less attractive for Protection Warriors/Blood DKs. Obviously this isn't something they can fix this expansion but I hope that they can eventually just get rid of dodge/parry on gear and make crit/haste attractive for all tanking specs. It's much more enjoyable to gear that way if you can get away with it because going pure dodge/parry is boring (and generally wrong).