Like tzs says, you want to get a comfortable health pool before you focus on anything else (because you still want to give your healers time to react), but mastery is a legitimate option at that point.
But a quick look on tankspot shows the general consensus is:
Reforge to mastery, or avoidance if you can't do that.
Gem for mastery, or a mastery/stam blend.
That's pretty much the gospel of maintankadin too, with some people even going so far as to ignore any means of additional stamina (reforging, gems, chants, and even trinkets) in favor of mastery when possible and a dodge/parry blend when not.
It's really not new theorycraft, but old (school) - the concept is that unblocked hits in Cataclysm are basically what crushing blows were in BC. So you accept a smaller health pool in order to maximize your combat table coverage, so you take fewer spikes. This makes you more consistently healable and in less danger of a string of bad RNG.