A few have been confirmed. But we won't know all of the previous ones until the game comes out. Pokmeon like pikachu and leafeon have already been shown.
Update: Yes, you can catch all the previous game's pokemon once you have the National Dex.
Of course I expect the regular geodude, onix, pikachu, machop, abra, ponyta, and psyduck should all be avalable at some point during the game.
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