Earlier quoted context omitted.
You are right. The first iteration however is 16bit and is very close to MS-DOS in terms of compatibility. Moreover, any OS that can handle simple disk I/O ops could be considered a DOS system too, innit?
Correct, there is a difference between MS-DOS and IBM-PC compatible and a DOS (ex: all the DOSes that existed for Amiga/Apple II/Commodore etc). There are many DOSes (and even MSDOSes, because yay early PC era incompatibilities!), but there is a very dubious list of things needed to be MS-DOS and IBM-PC compatible. You can probably do it if you're willing to setup a hypervisor and emulate some hardware. NGL one of my…
On the other hand, did you see https://github.com/FlyGoat/csmwrap when it came up a few weeks ago?
* https://news.ycombinator.com/item?id=44101828
There are already projects to provide replacements for the vanished Compatibility Support Module.