The documentation for FlexOS 1.2/1.3 is available on Bitsavers. So someone could re-implement it.

The build kit for CDOS-68k 1.2 (aka FlexOS 68k) is available ob Gaby's site.

I worked for an OEM in the 90s, and we used FlexOS 286 (and 386) ver 2.2/2.3 on some custom systems, including an ePOS system.