One of the things we wanted to do with Halo 4 was introduce a progression system that allows players to unlock things that not only change the way their character looks but also the way their character plays that empowers players to make choices that have a meaningful impact on their gameplay experience in multiplayer. Thats a big change, but its one of the things were most excited about.
Yep, that's the main thing I've been wondering about as well. It's been said that they're not "perks", but calling it a "gameplay-altering progression system" doesn't make me feel any better. It's too early to make any kind of opinion, though.
Yeah I certainly hope we hear more soon. I could honestly not see another frame of single player (other than hopefully cinematics cut together for ads and such cause using CGI or live action for ads blows), but we know very little about multiplayer other than some teases really.