The direction I'd take is to integrate community maintained allow and block lists to prevent people from creating new issues or PRs.
Another option would be a limit on the total number of open issues and PRs on the repo (not just per user) so that someone wanting to open a new one may be forced to work on issues and PRs from others first if they want to be able to submit anything of their own. And then have different limits for those on an allow list, or those that are financial sponsors.