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.

You could use a "OTP" to provide this: give out tokens ("OTP"), anyone with that token can submit, keep a record of the user (eg github username, email address) and token, run a bot to delete submissions that don't have a valid token, check the token+user pair, if there is a mismatch blacklist the user that token was given to whilst removing the PR.

My community does something vaguely similar, where you get credit for having bugfix PRs merged, and it's deducted when you get feature PRs merged.