Earlier quoted context omitted.
We don't need more POSIX copies. I would rather see someone take D, Rust, Swift, whateverX and implement something modern, following the concepts explored at Xerox PARC, ETHZ and MSR in terms of OS architectures and development environments.
It sounds you like you asking for more toy OSes. Supporting POSIX is necessary if the designer wants the OS to run real software.
Pjmlp (correct me if I'm wrong) would rather see exploratory endeavors rather than Yet-another-POSIX-impl. (And for the sake of argument, should that new platform garner steam and you absolutely, 100%, completely and totally need POSIX support! you can get pretty far creating PE/ELF on a non-POSIX OS with an emulation layer with ~3-4% overhead[VMware had a few whitepapers on it, and Unity is a component in production that demonstrates such behavior])
And if he were motivated enough to write a POSIX impl from scratch, while not trivial, it shouldn't be too hard (see: BusyBox, Yocto/Poky, hell, remember the NetBSD days? Any idiot could port to platform foo in a weekend.)