It still baffles me how people speculate, not only whether a Pokémon is OU, but whether its hypothetical evolutions will be OU. I mean, folks, we know nothing about how the X/Y metagame will be and what attributes will be important (remember, for instance, how important a Rock weakness became in the transition between generations 3 and 4). We also know nothing about how the discussed Pokémon will perform, not only in relation to the rest of the 'mons in the game (which arguably is the sole deciding factor for whether a Pokémon is OU or not), but not any stats, moves, anything to even know how it would be even in the current metagame. You might as well ask how the middle stage between Fletchling and Talonflame would perform in Gen. VIII RU, or for that matter how good Chespin would be in the next Super Smash Bros. if they added a Kalos trainer as a character. The answer - obvious to anybody who bother to think things through - is "insufficient data". It's not worth discussing until we know more.
But if we absolutely want to speculate, I think it's a given at this point that Fennekin will have some sort of psychic connection upon evolution. Either "Lucario style", as in an implied typing granting it specific powers, or a partial psychic typing. Note the lack of a capital P, it could be any one of Psychic, Ghost, Dark or even Fairy (since we know so little about what Fairy types actually do, we can't rule it out yet).
Chespin is a wild card. It could evolve into pretty much any typing without surprising me much (OK, Electric or Ice would be unexpected, but...). People keep throwing out Rock, Ground, Fighting and Dark as likely typings, and they all seem equally plausible. Still, that doesn't mean those are the only options.
Froakie certainly looks "airy" at the moment. The only flavour text we have about it mention it's a good jumper, and it likes bubbles a lot. I can certainly see it being part Flying type, but on the other hand, both Blaziken and Grovyle have been featured as excellent jumpers, and neither of them can fly. If I was forced to do a prediction, I'd go for a floaty bubbly flying cloud frog thingy (Water/Flying), but pure Water and for that matter Water/Fighting wouldn't surprise me either.
Let's not forget Tepig, though. Judging from the looks of it alone, very few could have guessed it ended up part Fighting upon evolution. Myself, I was thinking Ground or Dark, hoping for a badass quadripedal boar for the longest time. Since I saw Pignite and Emboar, I've decided to be extra cautious when speculating about typings.