Seriously, I don’t understand the point of the article, if there is one.
It seemed more like a confused enumeration of systems which are POSIX conform and in the end it talks about Wayland.
Is the point that Wayland breaks compatibility with X11/X.org and is mostly a Linux thingy? (AFAIK FreeBSD is working on a Wayland port, but no one else.)
Anyway, I am a happy Wayland user for several years now, although I am of course unhappy about the split with the *BSDs, OTOH most 'NIX software nowadays uses so many Linux APIs, that Wayland is IMHO no big game changer when talking about portability anyway.