pw: shield is still affected by mastery and it might look like disc will be going back to bubble spamming. however, stacking crit helps to proc more DA.
OK. Back in Firelands, Crit was, mathematically-speaking, an outstanding stat for Disc. We weren't using much PWS, so Crit affected most of our healing. It was the top throughput stat for PoH overall (or at least roughly tied with Haste, depending on your other stats): it gave us 200% heals and 300% DAs. And it wasn't half bad for Atonement and Penance. But most importantly, it blew all the other stats out of the water for DA stacking, on average. And DA-stacking was what we primarily did. Those giant crit DAs were pretty much guaranteed to be consumed, because we could roll them reliably. And we were spamming PoH on full-health raids for DA anyway, so crit, in theory, should have been awesome. The stars had aligned.
And yet people still didn't stack it. The prevailing build was Haste/Mastery - even though, mathematically, mastery was a far inferior stat, and it barely did anything for DA. The consistency of what it actually did, especially in those important moments where we needed PWS, was more important.
Now, crit isn't nearly as good as it was then. It does the same thing for PoH as it does for all your other spells: proc a bunch of overhealing and some unreliable, short-duration shields that have a fair chance of just falling off unused. And you won't be casting as much PoH anyway, because you won't be spamming it on full-health groups, so your crit doesn't even have an opportunity to pull its weight. Meanwhile, you'll be casting significantly more PWS (even if you aren't full-on spamming it), which heavily favours Mastery and devalues Crit. And you'll be using more Atonement than was used then, which favours Haste.
So...no. Don't stack Crit.