The auto-merge would likely be controversial, related [RFC 0050] Merge bot for maintainers by FRidh · Pull Request #50 · NixOS/rfcs · GitHub. I’m not sure how useful the labeling is, as you yourself said the majority of such trivial PRs are bot PRs anyway. One downside would be that prioritizing such a label would create perverse incentives, making people try to please the labeling algorithm and avoiding refactorings.