Are there any major distros (or even minor distros) that haven't committed to the /usr/-merge at this point? I know Debian has been having issues, but for the most part that decision has been made.
Debian didn't really have any issues with it either, merged /usr is the default since two stable versions ago already. There were just some troubles with internal politics around the topic.
Debian has merged /usr too. At least my current Debian 12 install does, and I'm pretty sure it had it before I upgraded it from Debian 11. I believe Debian's problem is (was?) only with migrating existing pre-merge installs.
The only "problem" Debian had was that dpkg maintainer had differing opinions on how the merge should have been done and used dpkg as a vessel to express those opinions. Merged /usr was already available in stretch, is the default since buster, and support for non-merged /usr has been dropped in bookworm (all non-merged systems are converted on upgrade now).
