I feel like GitHub should have a system where you can give out tokens that are valid for e.g. 1 PR. If someone shows to engage in meaningful discussion and has a good idea to address an issue/feature, you initially give them one PR token. If the PR is of good quality, you can give them a few more, until they are contributors that can just create PRs as they like.

A similar system would be nice for issues, though I'm not sure what it'd look like if issues are the springboard for contributing PRs.

Not likely to ever happen (as others said), GitHub/MS want to sell CoPilot subscriptions/tokens and LLM-generated PRs are a part of that business model.