Honestly, I'm hoping that the starters are dual-type, preferably Grass/Dark, Fire/Psychic, and Water/Fighting. I'm not pulling this out of my ass, either; Fennikin appears to use a Psychic move, given the colour scheme and the wavy animation of the attack, and Chespin seems to use some kind of slashing move, which resembles the move Night Slash. The only one I'm really iffy on is Froakie; it's attack is obviously physical, but doesn't have an discernible type. However, given a Psychic-type and a Dark-type, the third starter would be Fighting-type, as they form a trio similar to the trio formed by Grass, Fire and Water. In addition, due to the way that it's set up, there is NOT another Fire/Fighting-type starter (thankfully) and each starter's secondary type is strong against the one whose primary type is strong against it, thus forming, not just one cycle between them, but a second in the opposite direction of the first.
Now, this is all still just speculation, but I don't think it's entirely unfounded. Well, one way or another, I'm SUPER excited for the sixth generation!