Its never been bloated since only a portion of existing Pokemon are in each region. I'd find it very hard to look forward to future pokemon games without new additions, they're the main thing to be excited about in a new generation.
New game, new Pokemon. That's what keeps it interesting.
They don't need to commit to supporting every single Pokemon every single gen though. Each new generation it's fine if only certain Pokemon make it in. As long as they rotate them and keep a nice balance of new and old.
I hope people realize GF does cut Pokemon from games, as in, they don't make every single one of them available in a game. Just look at Glameow's availability for an extreme example of a Pokemon that barely exists in the wild. I don't know how many Pokemon exactly were available to catch in USUM, but it certainly wasn't 800.
So in practice, GF already does avoid bloating games with lots of Pokemon. Now, if what you're asking for is GF to excommunicate certain mons from the realm of canon, that's not going to happen.
Please, tell me how? Because BW2 has 151 gen five pokemon while every other gen is around 30-40 pokemon. A varied amount of pokemon, but gen five still has the spotlight on them. A huge difference when compared to gen six where while more varied the new pokemon are harder to find, and also have less when conpared to another gen. Next your gonna tell me Johto didn't also had a Kanto bias, and all the johto pokemon were easily findable...
So in 20 years they've created 800. In another 20 there'll probably be less than double. I can't even imagine the series in 20 years. I'm sure they'll figure something out, probably just slow down the amount of new Pokemon without necessarily capping it. I just hope they go back to longer periods for a generation to exist and cut out the "third game" bullshit of making people buy a new game for the same game + additional content.