Yes, fully agreed.
Would you mind adding a PR to adapt the PR template? A concrete proposal is always easier to evaluate than questions or opinions, and much more likely to produce a tangible outcome.
A minimally invasive change would be to provide a section at the end:
# How to test this change?
<!-- provide instructions to reviewers -->
The PR thread is an abomination, and in my opinion quite pointless: a PR should be opened (or put out of draft mode) if and only if it is ready for review. Picking PRs for review should not be based on recency, but some measure of importance (as proposed here: Improving Nix developer experience). Following up on changes should follow a well-defined process that can already be managed entirely through GitHub via notifications.
The PR templates are also way too noisy and would benefit from some refactoring. But that’s just my two cents of ranting about problems I will probably never get around to address myself.