I'd love it if Froakie ends up as Water/Dark or Water/Fighting. It looked as though he was using a Fighting type attack in the video but we really don't know. It could have been using Beat Up. But I'd love it if Froakie was the half Fighter. You know, just to break tradition.
Fennekin could work as part Ghost or Dark. I wouldn't mind Psychic, either. But if it ends up being half Fighting, I won't hit any forums for about a month. Or however long it takes for the fallout to clear.
I'm not sure about Chespin. Grass/Poison has been done and Grass/Ground would have a severe weakness to Ice. I just can't think of a good type that could help Chespin out. (Man, I'm pretty glad that it's not up to me to figure this sort of thing out. I would stink at it.)