See also Thread "Git release notes merge conflicts" on wikitech-l (April 2012). Several ideas for a format and automated tool have been proposed there.
However the discomfort and some people neglecting to include release notes does not justify anything. Until and unless we have a different tool, one is expected to include release notes. You'll just have to deal with it, whether you like it or not. If you don't then the change doesn't get merged (it is trivial to amend a patch and add release notes).
You claim of it being "almost never respected" is simply untrue, there are only a small number of changes from relatively few people that don't provide release notes when they should. Most people do when they should.
By the way, I don't see how Talk:Gerrit/Commit message guidelines#Bug number in commit messages is relevant? If anything, moving them from the subject to the body keep the raw git-log easier to scan. More on that over on that talk page.