I got this idea after reading Blessing of Kings excellent post on Chill of the Throne (aka Icewell Radiance).
Basically the best way for Blizzard to address the high avoidance problem is to remove Plate Tank gear in the next expansion, and put all Tanks in the same position of sharing DPS gear that Druids find themselves in today.
The first steps towards this have already been taken by Blizzard's announcement at Blizzcon that Defense is going away in Cataclysm. All Tanks will have a Survival of the Fittest type talent that makes you uncrittable. So already we won't see any Plate in Cataclysm with Defense.
Defense adds Parry and Dodge so already Cataclysm tanks will have lower avoidance. But it won't be enough. Let me show you why.
A naked Level 80 Blood Elf Paladin has nearly 11% avoidance, and that doesn't factor in another percentage or two from the 400 defense you get. (Every character gets 5 defense per level.) So already we're at nearly 13% avoidance. Combine that with talents like Deflection and Anticipation and a Tank is already sporting near 25% before he puts on his first piece of gear. Let's add in some raid buffs like Kings and Mark of the Wild. Let's also debuff the Boss with a hit debuff like Insect Swarm or Scorpid Sting which gives the Tank 3% more avoidance.
We can see that before you add one lick of Dodge or Parry from gear, a tank is already at or near 30% avoidance. This is actually MORE than GC said he'd like to see in the first tier of Cataclysm raids.
So what if, as Rohan suggested, the Developers do not put any Parry or Dodge on Cataclysm tank gear.
Then what stats do you have left to put on the 'tank' gear?
Yes, there are 'block' stats. Remember that the Developers are also changing Block to be a flat percentage, so we don't know how Block Rating/Block Value will work.
If we ignore Block for the moment, or assume Block will scale off of Strength, then what does that leave us with?
Expertise, Hit, and Strength.
What's remarkable about those stats? Yep, they are ALSO DPS stats. In fact, the only DPS stat you are missing is Critical Strike.
Now, how could we address Critical Strike in a way that would work for both DPS and Tanks?
What if we put Critical Strike on gear in the form of Agility? Now the Plate gear in Cataclysm is itemized with Strength, Hit, Expertise, and Agility. It should work for both Tanks and DPS. So in the same way that Rogues and Ferals share DPS Leather, Plate Tanks and Plate DPS can share all Plate gear. There would be much less 'wasted' gear in raids, and less gear to clutter up the loot tables.
Tanks will still prefer one handers while most Plate DPS wants two handers. Tanks will still be the only ones going for Shields, at which point it might make more sense to put them on vendors considering that only 1 spec of 2 classes even uses Tank shields.
So how would this affect avoidance? I believe it would keep Avoidance from going up too much each raid tier and the Developers can better keep it under control. If it starts to get away from them, they can tweak the Agility to Dodge conversion again like they did earlier in Wrath.
So what do you think? Would the 'Druid' solution work for Plate Tanks?