It would be very helpful to be able to programmatically block/unblock mergeability of PRs without being tied to a particular commit. The only APIs available for doing this are the Commit Status and Check Run APIs, both of which are tied to specific commits.
For example, enforcing that a PR body must contain certain things, etc. This has nothing to do with a particular commit.
This sort of functionality seems to already exist for certain built-in things (such as required reviewers, etc.) but there’s no ability to create/update arbitrary status checks for PRs.