Dr. Awkward said:
It seems to me to look like:
Round 1: Hey guys, I'm going to eat this dude's brain now. I'm gonna need a second here.
Round 2: Okay, I'm almost ready to eat his brain. I hope nobody stabs me or anything while I'm doing it.
Round 3: I guess I'll eat his brain now unless anyone wants to try to stop me. Last chance. Going, going... *whack* Oh, jeez. Now I have to start all over.
I suspect that the threat of brain eating is going to be largely the same as it was in 3.x: if the entire party is disabled, everyone's brains get eaten. Otherwise, it's too much of a hassle to try to grapple anyone and get beat on for the two or three rounds it takes to get into brain-eating position, giving up your other more potent attacks.