POSIX is more of a post-hoc thing, it doesn't really matter except for compliance - and then Linux isn't compliant. In practice you still need an abstraction layer.
If you want to use actual Linux features, you have to use Linux-specific interfaces. Of course a lot of applications don't do that, but that's besides the point.
The same is true for other UNIX (and non-UNIX) operating systems. They're not implementing new standards, they're implementing features to differentiate themselves.
> I will be controversial and say that Linux's utter dominance in the post-UNIX space may have been detrimental to the development of the ecosystem as a whole, limiting radical experimentation and preventing a much-needed reimagining of core computing paradigms.
Perhaps, but standards wouldn't help here - to the contrary.
