Moyes may indeed prefer Fellaini, but hopefully only as an upgrade for Ando and not as the "solution" to our midfield problems.
If we were talking about an all-prem XI player that would be one thing, but I don't like the idea of a new manager bringing in one of his former players to join the club. Can't put my finger on it, but it doesn't feel right to me.
On Alacantara himself, I can't say I've seen genius on the few occasions I've seen him play, but if he's good enough for Barcelona he's more than likelly to be good enough for United -- the keeper position being the notable exception.