Full patch notes are here

[Andres_Lonegrief]

It does say "As of 2.2", so maybe it will retroactively count earlier stuff for tanks who've been doing all the 8-mans before 2.2.

Edit: So wait, I guess mount collectors will just be grinding myth tomes on their DPS, i90ing their tank, and grinding turns 1 and 2?

I didn't interpret it in that way, but English isn't my first language so ...
Anyway I do hope you're right. I'm not a tank, but I know lots of people who deserve it and I'm not sure they meet that 200 high duty requirements