Well, this is sort of a stretch, but, I'm going to throw sort of a curve-ball speculation here:
People have been betting on the starter trio evolutions are probably going to be part Dark-Psychic-Fighting, or at least expecting that Fennekin's evo will be Fire/Psychic, or at the very least that Fennekin's evo won't be part-Fighting? What if that's a little too obvious? Game Freak really isn't. They love curveballs. I remember that the wildest guess people would make at Piplup's final form was of a Water/Flying penguin, but most expected a Water/Ice. Needless to say, Water/Steel was quite a surprise. No one expected silly Turtwig becoming Torterra. Some people only bet on Oshawott becoming a Water/Fighting samurai otter after we saw that rough sketch which showed Iris, Ash, Axew, Dewott and Servine, and Game Freak's designers even admitted they wanted Oshawott not to look like it would evolve into a samurai, AND that its samurai form weren't so straightforward in design. Obviously no one expected Tepig would become bipedal, much less that it would be yet another Fire/Fighting, or that Snivy would lose its legs and only its legs, or that the cute Mudkip would become that Swampert, or that sweet Torchic becoming Blaziken.
Well, I dunno, while it's fine to expect Chespin will become a hedgehog because of its names, there's no way we can be sure of their final designs or typing because we don't know what Sugimori had in mind when designing them, and we probably won't until a couple weeks before release, or perhaps a few weeks or months from now, when they might give some interviews on the matter.
With this in mind, What if Fennekin's evo will be Fire/Dragon? And I know, before someone says, "oh but that will be early dragons!" Take a look at Altaria and Vibrava -- they were available at level 35 in RSE by the 5-6th badge. If only Fennekin's final form is part-Dragon, then players will only get it at level 36 or so. You could get a Gible in Platinum by the fourth badge too, so it's not that far-off to expect Dragon as a starter's final form. The experience rates are also alike (Altaria was Erratic, Garchomp is Slow, starters and Flygon are Medium-Slow), so there wouldn't be any difference in the training.
While Altaria and Vibrava don't have the same BST of a starter (Altaria is 490, Vibrava is 340, starters are 525-535), even if the Draco evolution of Fennekin had huh good stats (unlike those two), I don't see how would it be unfair, considering we've had Technician Scyther in Platinum, Infernape/Staraptor using Close Combat in DPPt, Magnemite resisting everything in BW2 and Sturdy Sawk in BW. The only real problem there could be is "type design", but I don't buy it too much because I know that, as a kid, I knew Kingdra was a dragon, and it's a cool dragon!, but not as dragon as Dragonite, which was the real deal. I'm sure no one would think of DracoFennekin as anything more than "a cool dragon!". Unless, of course, people can think Dragons should be "rare", but again, look at Trapinch evolving to Vibrava and Swablu evolving to Altaria.
Maybe considering Fennekin's final evo will be Fire/Dragon, I would also bet on Chespin's final evo being Grass/Steel and Froakie's final evo Water/Ground; this way, Froakie can hit both SE; Fennekin hits Chespin SE but has some problems with Froakie; and Chespin walls the "overpowered" part of Fennekin while beating Froakie. This is... balanced, in my opinion. Sort of. It doesn't need to be perfect, never did, never will. Or maybe Grass/Steel and Water/Fighting; it also has a good, "different" dynamic (Froakie can't hit Fennekin SE but can hit Chespin's final evo; Fennekin's final evo beats Chespin's but can't touch Froakie's; Chespin's still walls the "overpowered" part of Fennekin's while still beating Froakie's, but can be beaten by both. Reminds me of Empoleon), and all three have excellent complementary types.