Too late? https://docs.freebsd.org/en/books/handbook/linuxemu/

Somewhere there is a dark timeline where the BSDs won, there are 50 commercial and open source variants all with their own kernel and userland. The only promise of interoperability is in extremely ossified layers like POSIX. There is, however, something terrible gathering its strength. A colossus. The great Shade that will eat the net. In boardroom meetings across the land, CTOs whisper its name and tremble... "OS/2."

Also, AFAIK SmartOS / Ilumos has had a combat layer for it, too.