I get the feeling Fennekin will end up bipedal. Or it'll pull a Slakoth and become bipedal in its middle stage, and then go back to being a quadruped in its final stage.
Froakie... is, like, the fifth frog/toad we've had so far. I feel like it's going to end up like a previous frog/toad Pokemon, unless its evolutions are combined with another animal--like, say, a salamander. That'd be interesting.
Chespin is begging to be a Grass/Fighting type, but I won't set my heart on anything (*remembers Samurott*). I think he'll stay bipedal. If he's combined with any animal, I hope it's a bear.
Interesting that the starters this time around are all commonly-used animals. Each one's animal basis has been used multiple times in Pokemon designs (I mean, if Chespin is a chipmunk, we only have Patrat, but if you broaden the scope to "cute rodents"...).