Just read this post on the EU Forums. So going to copy it here.
Can't say I disagree, it will be a nobrainer to go satin after this goes live.As you all know; mooncloth is getting a new 4 set bonus which basically means a 4 sec freedom each time you cast power word: shield. This is nice and very much needed.
However, shadow priests are also suffering from mobility issues and so far nothing is being done about it. I feel a little bit left out while disc gets all these shiny new buffs. Shadow 4 set bonus is already crap and no one is taking it. There's also a discussion on AJ atm where the majority will be taking the mooncloth set for shadow because the 4 set bonus really is that good that it outweights the stat loss.
So here we go again, another season where shadow priests will be using mooncloth.