There is no mention of User:Matma Rex's mediawikireleasenotes-driver which solves the problem. The only missing bit are automated rebases because Gerrit uses a Java implementation of merge drivers so developers have to "manually" rebase a change prior to merging. If the latter is a major nuisance, creating the missing Java merge driver feels like a much cleaner solution than Proposal 1.
Topic on Talk:Requests for comment/Release notes automation
Multiple technical solutions are possible to make release notes addition viable. None of them, alone, will make people actually add release notes, especially because most of the times release notes are needed for (some) users, whose use cases the dev(s) are not familiar with.
So it doesn't matter what technical solution is better in theory, but only what solution will create the highest social pressure for devs to actually bother adding release notes.