By making threat gen stats also generate resources that are used to actively mitigate incoming damage, the goal is to make tanks want those stats, rather than simply aiming as close to complete coverage of the combat table as they can get, reducing incoming damage to something as reliable and easily anticipated by healers as possible. Tanks currently value dodge, parry, and their mastery stats well over any potential threat generation from hit and expertise.
Since we've already seen quite a bit of the Mists of Pandaria talent calculator, we know that design of the new tanking system is probably fairly well advanced. We also know that the monk, another tank/DPS/healing hybrid class, will be debuting with the expansion. Therefore, it's worthwhile to examine tanking changes that could be implemented, even to stretch our vision of tanking significantly past where it is now and most likely past where it will go in Mists.
The interaction of avoidance and mitigation stats
First off, let's consider the current tanking order. Druids tank with dodge and mastery, which modifies their Savage Defense ability. Death knights tank with dodge, parry and mastery, which buffs their Blood Shield ability. Warriors and paladins both tank with dodge, parry and block, as well as each having a mastery that adjusts block, paladins using Divine Bulwark while warriors gain Critical Block. These are the only four tanks currently in the game, although clearly with the addition of the monk, a new variation will be likely.
One of the things that occurs to me on casual inspection is that warriors and paladins have a much easier time achieving total removal of unmitigated physical damage. With statistics undergoing diminishing returns, druids are at an extreme disadvantage (to the point of apparent impossibility, although I won't rule out a talented druid player going to lengths to achieve it) when it comes to reaching the 102.4% avoidance/mitigation number that means no unmodified hits will land from a skull-level boss. Death knights can at least use dodge and parry, but even then it seems unlikely.
Since two tanks can combine dodge, parry and block with an eye toward achieving this goal and two cannot, stresses on the unique compensatory mechanics of druids and DKs become apparent. No matter how hard these two tanks work, they'll always be more vulnerable to streakiness. They can get lucky and mitigate a lot of damage if Savage Defense or Blood Shield are up, but if rune tetris doesn't line up or Savage Defense doesn't proc (50% chance, remember), then they can get blasted in the face with randomness.
The flip side of this issue is mechanics that completely ignore physical avoidance/mitigation. These effects (many bosses have magic damage of this type, often a very large damaging ability that also bypasses armor) tilt the scales in favor of effects like Savage Defense/Blood Shield.
True, unadulterated hatred for the roll of the dice
Tanks hate randomness. It's necessary for gameplay -- there has to be a chance things will go bad or encounters don't even need to be experienced, after all -- but every tank wants to reduce that chance they'll take a big hit their healers aren't ready for down to zero or as close to zero as they can arrange. You can't blame them for that. Tanks are just playing the hands they're dealt, and it's a fact that bears and DK tanks are disadvantaged not by their skill but by an inability to play with their stats the same way other tanks can purely because they don't have the stats to play with.
By moving all tanks to a more active mitigation system (Savage Defense and Blood Shield both require the tank to act, to score a critical hit or heal themselves with Death Strike), random chance can be made an element of all tanking again. Not only do offensive stats become attractive to tanks because they're required for mitigation, but also they become attractive because it's impossible to gear for total passive unhittable status.
One imagines adjusting tanks further, however. At present, two tanks enjoy the ability to reach for total coverage of the hit table due to their possessing three avoidance or mitigation stats (dodge, parry and block) and a mastery that allows them to increase block. What if no tank could do that? Imagine if, say, paladins could dodge and block, while warriors could parry and block. You would then have a system where no tank could achieve passive coverage due to diminishing returns (or at least not as easily) and where every tank but druids could have two out of the three avoidance/mitigation abilities.
For that matter, allowing druids to parry or block wouldn't be out of line, either. If bear mobs can parry, why not bear tanks? Redistributing stats in this manner would give each tank a more unique feeling while allowing for commonalities. Since dodge and parry effectively do the same thing (completely avoid damage) while block reduces damage by an amount, tanks that have block and an active avoidance can be allowed to stack their block chances upwards more drastically than those with two active avoidances (bears, DKs and possibly monks, in this scenario) to compensate.
Giving more room to move
In addition, this gives tanks more room to play with active stats like hit, expertise, and perhaps even crit or haste. Now currently, all three plate DPS want exactly the same stats on their tanking gear, more or less -- dodge, parry and mastery. If paladins could no longer parry and warriors no longer dodge, of course, this would require some changes. Just as block rating went away in Cataclysm, we'd need some redesign of tanking gear to keep it viable for all three tanks in plate.
One possibility would be to have dodge and parry removed from gear entirely and to have all tanks derive their dodge and/or parry from their active stats. Parry easily derives from strength (since it does already), and one could imagine paladins gaining dodge from strength from a talent that converted it.
Tanking has come a long way in seven-plus years. Crushing Blows, once the mainstay of how bosses threatened tanks, have long since departed. Defense is likewise gone. Tank fights involve a lot more placement and awareness, responding to abilities, gathering adds, trading bosses, even using cooldowns proactively to weather large bursts of otherwise fatal damage that would ignore the tank's armor and other mitigation or avoidance. We're even now seeing gear with set bonuses that allow tanks to extend these defenses to their party or raid.
In the future, tanking may continue to develop away from the original conception of a target for enemy ire who stands in one place and keeps mobs busy and toward a defender who can shunt or redirect damage, perhaps going so far as to turn the damage a boss intends for another player back onto the boss itself. (Linking such an ability to active stats like hit or expertise would again increase their value.) Tanking is already fairly divorced from having to work to keep mobs angry at the tank by this point. Why not make a tank less of a meat shield and more of a spiked wall for his party to dive behind?
Since we've discussed some ideas and concepts I came up with, it's now time to throw the floor open to you. Don't just content yourself with what I've suggested. What ideas come to mind for you? What would you like to see for tanking? Greatshields, one-handed tanking polearms ... the sky's the limit here. What could the future bring?
World of Warcraft: Mists of Pandaria is the next expansion, raising the level cap to 90, introducing a brand new talent system, and bringing forth the long-lost pandaren race to both Horde and Alliance. Check out the trailer and follow us for all the latest MoP news!