- Threat generated by tanks has been increased from 300% of damage dealt to 500%. What this means in practice is if your tank is doing 5k DPS, you'd need to do over 25k DPS to pull threat off of him or her. (You need to do roughly 110% of tank threat to pull once he or she has aggro, so you'd actually need to do 27.5k DPS to pull off of a tank doing 5k DPS.) This change was hotfixed in, so if you're noticing your tank is suddenly doing a lot more threat per second, that's why.
- The way Vengeance stacks is going to be streamlined. Vengeance currently ramps up somewhat slowly. In the current model, every time you take damage as a tank, you gain 5% of the damage you take as attack power. So if you're hit for 20,000 damage, you gain 1,000 attack power. As you take more and more damage, this stacks up to a maximum of 10% of your health, so for a tank with 165,000 health, this caps at 16,500 attack power. In the new version, when a tank takes that 20,000 damage, he or she will gain one-third of the damage of the attack as attack power immediately, or 6,600 AP. This is more than six times as much attack power gained as in the current model. Vengeance will otherwise work the way it does now.
This is really groundbreaking stuff, and it means that patch 4.3 will see the complete dismantling of the legacy of vanilla WoW tanking design. Once, gaining and keeping threat was the most important role of the tank, more important even that survival, and many endgame tanks were warriors 31/5/15 specced into Defiance in the protection tree to ensure threat. These changes can be seen as driving a final nail into that kind of tanking's coffin.