The state of binary compatibility on Linux and how to address it

Why don’t the authors release a distro that actually implements their own proposal?

Say, based on (perhaps on pieces of) musl, to be more straightforward to get things going?

This is simply too complex. There are quite a bit dependencies on Glibc and other GNU-based behavior.

What you're actually asking from them is creating a new Android or Chrome OS i.e. recreating the entire userspace. "Just split up musl" will not work. How the system headers work needs to be redefined. This is basically a complete redefinition of entire API of all Linux programs and libraries. Which library will supply unistd.h or any of the sys/whatever.h? Any interdependencies? I think even POSIX itself can be hostile against this. So the fix will have to deviate a lot from that (that's probably why Windows cannot be made POSIX easily either).