With Attack Power on gear gone, and classes more directly gaining AP from stats (which to be fair is pretty much how most tanks do things now) and even more importantly, with Defense gone and all tanks gaining their critical strike removal from talents as Druids do now, we could very well be looking at the end of tanking gear entirely. It's possible, perhaps even likely that in Cataclysm your DK, Warrior or Paladin tank will wear the same gear (perhaps switching in a shield in the case of warriors/paladins) to tank as he or she does to DPS. For an idea of what this might look at, we can consult the current itemization of Druids with the Survival of the Fittest talent.
After all, once you've removed stats like AP and Defense from gear and had them derived purely from stats, the temptation to keep the process going and simplify gear even more must be strong. If Dodge, Parry and Block were entirely removed from gear (we already know that Block Value will be removed and Block will remove a percentage of damage as some of you suggested in our past discussions of Block) and your Dodge, Parry and Block were simply based on your stats (each class could be tweaked in one way or another) that gear could be itemized to provide DPS and tanking stats in one item. A piece of gear like the Undiminished Battleplate, for instance, is already almost flexible enough to be used by DPS or tanks (my tauren wears it as a threat piece as he has enough defense without it to be uncrittable) - in a system without defense it would only be more attractive.
Another potential issue with the loss of defense on gear and the use of talents to compensate is one of off spec off tanks. Right now, an arms or fury warrior or ret paladin or DPS spec'ced DK can still slap on their tank gear and be uncrittable, making them reasonable substitute tanks in an emergency. (I did this tonight on Auriaya in fact, throwing on my sword and board and SBV set so that I could offtank one of her annoying Sanctum Sentries and still equip my DW weapons afterwards,) If tanks are now uncrittable purely through talents, then either those talents need to be available fairly easily so that Arms and Fury/Ret/various DK's can pick them up and still off-tank (and then we run into the difficulty of PvP balance) or you simply have to accept that when you need to offtank, you have to switch to your tanking spec.
There's also reforging to consider. We saw it mentioned in the Class, Items and Professions panel, and it has the potential to be a real force in tanking itemization. Since Engineers, Leatherworkers, Blacksmiths, Tailors and Jewelcrafters will all have their own Reforging specializations, each tank will have the potential to alter certain drops. With the ability to reduce points in one stat on a drop and put it into a stat that the item of gear doesn't currently have, an item like the Breastplate of Frozen Pain could be turned from a DPS chestplate to a tanking one by, say, removing the critical strike rating and replacing it with Expertise or Dodge (if Dodge stays as itemization) or what have you.
Finally, for two of the four tanks, a stat that is currently relegated to trash tanking and threat will be completely revamped. Block Value is gone, and a successful block will reduce incoming damage by a percentage, meaning that the stat will scale to be as good against a boss that hits for (as an example) 20k as it is against a trash mob who hits for two hundred. In fact, if in the new system a successful block reduces 20% of an incoming attack, then it is actually worse against trash than it is now (right now, a high block rating/block value set can completely remove all damage from a trash pull) while being much better against big spikes of damage. (If a current block takes 2k damage off of a 22k hit, you take 20k damage. If instead a block reduces an incoming hit by 20% that's 4.4k damage off of a 22k hit, more than doubling the amount absorbed. This is a big change, and it will make Block a valuable stat against bosses, especially if you can get more taken off of an attack by stacking the stat in some fashion. This does argue against losing stats like Dodge and Block from gear, however. It would still be possible to do so by simply having Block (as an example) calculate from Strength and Dodge from Agility.
As of the time this is being written we haven't even heard any specific class changes for the four tanking classes and we're already seeing a paradigm shift for tanking gear. More details on each class will provide a sharper focus for the future of tanking in World of Wacraft, and I for one am dying to hear more. Just from what we have so far, Druids will be the least changed as other tanks move towards a similar system.
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