And yet we continue to pretend not to understand why average users of WordPress are confused as to what it is. There are a lot of people already doing "Preparing for WordPress 5" talks, articles, books that it shows regular users don't understand our versioning scheme.

Neither do we.

Until recently, every X.Y version of WordPress was a "major release." Because we stated 5.0 would be the Gutenberg release, we broke that and used a couple of X.Y.Z versions that would've normally been maintenance versions. We broke our own versioning scheme.

I have no problem with shipping the PHP 7.3 compat work alongside Gutenberg. That's just fine. But we need to remember - users and developers are two (often) completely different groups of stakeholders. A user sees WordPress increment from 3.9 to 4.0 and thinks it's huge (It wasn't). They see the move from 4.9.Z to 5.0 and also think it's huge (It likely will be). But we slipped some pretty large things in there as "maintenance releases" as well ...

4.9.9 should still happen. It's still a bugfix release. That's what the .Z versions are for in the first place. There's zero reason to wait.