I've tested pretty much all tank classes on beta, either in raid encounters or dungeons. One thing I can confidently say is that if things are to stay as they are currently, monks won't be an attractive tank for mythic progression. We are once again being bottlenecked in our spell usage due to the lack of haste, and the low base armor of the spec coupled with extremely shitty mastery makes for some really hefty hits from bosses. I am not sure if this is going to be a trend from now, but as things are looking right now I won't be playing brm for the first raid tier .