With the new Beta information up the change, or rather lack thereof, that interests me most is that of fear. Druids got a new way to break fear, Warriors can stance dance their way out of it every 30s, this leaves the other main tanking class* as the only one with no way to avoid fears. I won't consider Death Knights since I don't know enough of them to really say whether they are Main Tanks or not, their lack of armour seems to suggest they might have a niche role in tanking that isn't specifically Main Tank (who by definition should be able to tank anything), however this needs a real look at instance / raid tanking to confirm.
Getting back to my point, Paladins, the Defenders of the Faith, Warriors of The Light, Faithful Champions, turn tail and run at any chance we get. In the Warcraft Games Arthas stood amongst his enemies (with Uther and many others), and fought, ressed and even mass resurrections his followers. In short, the background idea makes the idea of a Paladin running away from at least Undead and Demon fears unlikely, these are the enemies of the Paladin, why would we run. Giving us no way out of fears also means that our use as Main Tank needs to be considered closely, why give a Paladin a slot on Archimonde as tank when a Warrior won't eat up your Fear Wards (ok I can argue why, but after seeing the fight its really not a dps race, its a "don't stand in fire", "Press tears hot key before dying" fight). The answer is that you don't, you take pity on your Paladin tanks and let them leech or respec Holy for the night, and thats not a good situation for a tank to be in, the viability on any fight must be considered for there to be a reason to take you along, and for the game to really support 4 tanking classes.
What fights should be like is Reliquery of Souls, part 1 favours a Paladin in block gear, part 2 really doesn't favour a Paladin, and part 3 really favours a Paladin, its slightly unbalanced in favour of the Paladin here but the idea is sound, a fight which favours at least 2 classes of Tank and can be tanked by any of them. Archimonde on the other hand, his fears hitting the Main Tank doesn't add anything to the fight, for a Warrior its a button click, for a Paladin or Druid its a Fear Ward. Hitting everyone else means you need to worry about the Main Tank dying, but hitting the Main Tank simply means the boss might run around a bit and maybe crush the tank, its not a real issue, its a mechanic that pretty much penalises lag, the penalty is the same if the tank stands still and everyone else runs around, except that making the tank run reduces the truly viable tanks down to a Warrior.
Stupid mechanics are fine, some of them are fun and interesting, Kael'thas Sunstrider making it hard for melee to hit High Astromancer Capernian is fine, because the two warlocks that tank it can solo her while you go on with the fight. Making life harder on the tanks, and making sure that two out of the three classes that could tank a fight are sub-par is not a fun mechanic, you don't tend to see people ever saying "A Warrior can't tank that", what you see is "A Paladin / Druid would be better", and thats the situation that we want to get all the tanks to, preference yes, bench warming no.
* At current the Main Tanking classes are Warriors and Paladins due to the availability of crushing blows which can severely mess up a Druid's day. This isn't to say they can't main tank, since I know they can but its a potential liability on things like shear from Illidan that most guilds would rather not deal with. The fact that both Paladins and Warriors lack a real not-tanking role also means that Feral Druids tend to get shunted into the DPS / tank when needed role rather than being allowed to tank fully, I would like to see all of the classes get a fair shot at this really rather than forcing off-tank status onto at least one class.