So, the answer to the question “Can Linux directly host another Unix-like operating system’s binary interface?” at the moment is “partly, experimentally, and impressively.”

As if there was any question on that? You can have Linux "handle" Windows PE binaries by telling it to invoke wine, dealing with a Unix-like scenario is a much lower bar.

The question is who is this useful for? FreeBSD has the Linux compatibility layer because it's playing catch up to Linux, but the Venn diagram of stuff FreeBSD can do but Linux can't is tiny, especially if extra special kernel feature stuff is stubbed.

Can anyone name a project that is BSD first, doesn't rely on BSD kernel features, doesn't have a native Linux port, and isn't a distro tool?