I've used MC as CC on occasion since vanilla as a priest healer, the only time it's been problematic was when it missed (though for trash of equal or lesser level that chance is pretty low).
Pretty much every time in heroic Magister's Terrace for instance, that last trash pull before Kael that non-raiders and pugs regularly wiped on when lacking or not using CC, I'd usually start out by MCing the Naga til it got killed, then running away and LOS giving the tank the opportunity to challenging shout or roar or have them run through consecrate. Plus I have fade. Combined that with having a mage or traps, we didnt wipe that pull near as much as when I was on my alts and we didnt have a priest.
In this expansion, for example the Vortex Pinnacle, when I run with a shadow priest, we don't need other types of CC at all. When you get to those big groups at the end with the grounding fields, he MC'd the adepts which have enormous heals. It was much easier than we expected the first time we tried it.