Thank you to everyone for weighing in on this! I tried to ensure your feedback was reflected in what ultimately landed in: Update the developer policy to mention release notes · llvm/llvm-project@009048a · GitHub
Also, I filed an issue about precommit CI testing Sphinx: Please test documentation generation on precommit CI · Issue #54998 · llvm/llvm-project · GitHub
I think this is a great, positive change. One additional idea might be to have a script that creates issues assigned to the code owner of each component (perhaps this mainly makes sense for backends/targets?) to review/finalise the release notes. The responsibility would be to do an editing pass over the notes, check nothing major is missing etc. This is a responsibility code owners have anyway, but having an assigned issue would help make sure it happens.
Hans used to send reminder emails to code owners for this, but I’d hope issues + a script to create them would mean less workload for the release manager.