it's my understanding that most distros by now have moved to have their stuff in /usr, though there might still be backwards compatibility symlinks of course.
Just don't put /usr on its own partition. What is the point anyway after we have merged /bin into /usr/bin, /lib into /usr/lib etc. Just put your operating system on a single partition and be happy.
You're kidding me right? Nobody ever bothers with that for anything else and the company I work at spends like more than half the time resolving stupid install breaking changes that nobody asked for. This would just be one minor extra thing on that pile, but at least it would make sense for once.
No reason to do it on embedded system. Lots of backward compatibility reason on servers/desktops.