First Gen starters.

[Cenewulf]

Will it be possible to capture Bulbasaur, Squirtle, and Charmander by the time the game is fully released?

 

[Darkfire]

It is an unknown
however you can mod your save file or the route conditions to get one now(or you can play my mod for a slight chance of catching them in specific areas

 

[DracoHouston]

i personally would like steven stone to give you a sinnoh starter and oak to give you a kanto starter after you beat red like in HG/SS versions. however, we aren't anywhere near that yet, haha, so there are no concrete plans

like darkfire said though, you can edit your saves