Oh god, the irony.
Earlier today we were joking and placing bets in guild on who would bitch about the new 20% MSs more: ret pallies or DKs. Both do very well in PvP and both pretend that they don't.
I highly doubt that these new MS effects will stack with the current 50% MSs. The only mildly successful shadow priest comps all include rogues and the only successful mage comp that doesn't include a rogue or hunter is in 2s: priest/mage. It is very possible that I am overlooking some, but I'm tired so screw it.