It doesn't affect the metagame at all. As far as the metagame is concerned, being able to catch all the Pokemon in one game is no different from being able to get all the Pokemon in one game through trading.
I think you may be a little confused as to what the metagame actually is.
STOP CALLING ME HOME ROWED i don't even gaf anymore
The closest we ever gotten, and possibly we'll ever get though I hope not, was PMD: Explorers of Sky when fourth gen was the latest generation. Even then it was still missing one pokemon, Arceus. Spin offs are probably going to be the only way it'll happen. Gamefreak is too event-only happy and as said they make more from two versions.