It would be a superset of POSIX anyway. POSIX is the minimum common denominator and should work with an ASR-33 teletype connected to a serial port.
Which never happened in 50 years.
Being POSIX compliant never prevented an OS from having excellent multimedia capabilities. Perhaps Commodore management didn't see the value of a Unix-like OS for a home computer back then and, when they saw it, with the 3000/UX, it was way too late for the 68K.
Hence NeXT, Irix, and NeWS examples I gave.
Yet hardly anyone cared about POSIX, rather whatever was on top.
I find it sad that Commodore didn't include CPUs like the 68020 and 68030 in base Amiga models until many years after their initial release. Maybe with a bit more revenue from higher end CPU models, Motorola could have put more effort into advancing the product line. How different a world it would have been if IBM went with the 68000 instead of the 8088.