I hope they'll include Heracross, Numel, Electabuzz and Magnemite, among many others
Any Gen III Pokemon that haven't appeared in any other regional Pokedex besides Hoenn's.
And also, i hope they would exploit that dna splicer stuff to more pokemon, having a Charizard-Hydreigon-Haxorus hybrid would just be Spectacular.
I really don't think (hope) this will be much of a thing, since the Kyurem + Zekrom/Reshiram Fusion seemed more of a storyline element than an actual new gameplay mechanism of the series. Making it possible to combine any 2 or more pokemon would make things way too complicated in my opinion.
Since Articuno and Latias are legendaries, they might be included as special post-game events, like in the newer games. I would love for Houndoom/Houndour to be included, he is a beast! Vulpix and the Ghostly family are pretty nice, so i hope for their comeback as well.
Some other interesting questions:
How large do you think the National Dex is going to be?
How many of these will be new Pokemon, how many old ones??