A lot of teams are not using tank specs as flag carriers anymore, this is a fact and I know from GM exp and talking in forums.
However with the new legendary tanking back in the game, tank specced players, who are already hard to kill, using it will have one other life saver, IF this cloak turns out to give you some sort of a shield of X% or Y value after taking a hit that would cause you to die OR somethings of the like.
Personally I think they will change for it because the procs from all other cloaks are significantly better for their specs then the tanking one is for tanking, because right now, in a lot of PvE content, tanks are getting hit constantly, and saving you from one attack that would kill you, which can always be avoided if played right (that's the point of it) is nothing because, if you are playing it right, you'll die from constant attacks because your healers couldnt manage to keep up and after getting saved by X attack, you'll still be at low health and probably die from the next attack.
This proc, right now, is merely good for content where there are abilities that must be dealt with by kiting or pre-shielding/CDs, on which case you will be able to just take the hit every 60 secs. It's just not anywhere good compared to the healing one, that makes you, throughout a whole fight, get extra healing from your overhealing, which is why I think it will probably change.
If it does change to some sort of what I said before, PvP spec tanks will definitly come back with this being BiS, as giving you an extra seconds after supposedly dying will give an extra chance for your healers to heal you back up, which can be game-breaking in any type of flag carrying game.