Well, when you think about it, Gen I and II Pokemon already kind of had their time with 4th gen, y'know? They took things like Magmar, Electabuzz, Gligar, Piloswine and gave them evos and heck, they even turned a slight head towards Gen III and gave the Ralts line a split-evo (as well as give Dusclops an evo). I'm honestly hoping that maybe this generation would lean a bit more towards Gen III for evos than anything else.
I just hope they don't restrict themselves to Gen4/5 pre-/evolutions. I mean sure, we've already seen a Gen 1 evolution (Sylveon), but an eeveelution is different, I think. I don't know, it would be awesome to see evolutions of some older Pokemon as well as newer ones yup.