Taunt swapping versus pressing a button to deal with death ray; it boils down to pressing a button at the right time, we all remember the first week where taunting the wrong dog or hesitating caused a raid wiping overload, and its considerably rarer that there's some mechanic where you're punished for not having timed your active mitigations (I can think of 3 off the top of my head, Sha, Tortos, Ra-Den), but both mechanics aren't really very fun. I feel Tanks need more "movement" mechanics like Will or Heigan or Shannox.
Or Marrowgar, I think Marrowgar could be a really interesting set of mechanics to tank again, between the constant frontal Cold Flames (I know that wasn't really intended) and the meteoring Bone Slice. you could have them both hit really weakly on LFR and on heroic have the cold flames timings be randomized in addition to the ramped up damage. Avoiding Horridon's double swipe is fun, but hardly challenging, i want there there to be a mechanic so that its done either to the left of his centre line or right of his centre line and/or that he rotates to focus the tank after each swipe dodge one, dodge the next, don't put his arse to the raid.