This is actually a good idea.

I mean, not sure if everyone wants that for their project, and there will surely be plenty of trade-offs.

But it would be a very good compromise: You (the maintainer) get only human-generated PRs in the canonical project, and they (pro-AI contributors) get a lower-threshold sandbox to play with. Best case scenario, you cherrypick the pre-filtered golden nuggets to bring back to the canonical project.

Precisely. Cherrypick nuggets from poo. It's there if you care to wade into it. May occasionally strike gold.