Tanks are getting buffed, this is great, but I see a huge problem now getting even worse.
Currently a major theory in tanking is Effective Health. The basic concept is that when your avoidance fails, how much damage can you survive? It ensures that no matter what the RNG does, you will survive. It can also be expressed as time to live, or time to heal, showing how quickly healers need to be landing heals. It is pretty much the standard method of gearing when trying to move rapidly through content. The stats it considers are armor and health, though defense has a side role in that your effective health plummets if you are able to be crit, so get that 490 defense! Armor can't really be stacked very much; there are few enchants, no gems (unless you're going to use agility at 2 armor per agility), and the gear with extra armor tends to either be rings or just plain better gear. But stamina (health), that can be stacked. There are several enchants, many trinkets, and most importantly: gems.
EH plays a huge role in the habit of players to gem for stamina, endlessly, almost completely ignoring other stats. There is also the influence of players just looking at health since avoidance is invisible to outsiders, but I'm going to focus on EH. What's wrong with this? Well, I can't honestly give a good reason, it just feels wrong. It seems strange to have one gem be incredibly valuable while the others mostly fall to the side, relegated to a few paladins still going for uncrushable. It seems wrong that socket bonuses are constantly ignored, ironically they are sometimes even stamina. Gems were supposed to provide customization, instead they're just a massive gold sink for more stamina.
From the looks of it, WotLK is only going to make this worse. I wrote before about time to live, or time to heal. Time to heal means that the tank has to get this much healing in this much time, or he's likely to be dead. Avoidance helps, or does it? It can't be relied on, so healers will be healing anyway, avoidance just means they overheal. Downranking used to help, dropping the healing output a bit for lower overhealing and greater efficiency, or at least lower mana usage so that regen could keep up. With downranking gone, but time to heal not going away, healers are going to end up doing massive overhealing unless they are all getting new mid-size heals which can be spammed. The overhealing could be avoided by just requiring more healing, making bosses hit even harder, but that's just going to push EH requirements even higher, making worse the problem of stamina stacking to the exclusion of other stats.
Something has to change. Avoidance should mean something, not just be a source of overhealing and missed opportunities for rage. It's time to put an end to boss damage just getting higher and higher and pushing tanks into ridiculous gearing. Effective health must die.
 An easy way to reduce the need for effective health, while maintaining damage outputs, is to make bosses swing softer but faster. This would also make blocking more significant for mitigation.
Guest post: The mind of a tank
12 hours ago