I don't think that the articles addresses the real problem with POSIX/SuS. The fact that SuS does not deal with GUI is feature, also there are no OS implemented

I don't think that the articles addresses the real problem with POSIX/SuS. The fact that SuS does not deal with GUI is feature, also there are no OS implemented complex syscall multiplexers on top of ioctl() for that, such multiplexing happens in hardware. (Try stracing glxgears, with my radeon it calls ioctl quite heavily, but only uses two functions, both of them are essentially "wait for interrupt from hardware") What I see as biger problem is that current Single UNIX Specification is that it essentially has nothing to do with UNIX. On the list of certified conforming systems, there is Solaris (which does not implement all the optional modules one would expect from something that _IS_ derived from SysV), z/OS and bunch of embedded RTOSes noone ever heard about. And if you look on what is required and how underspecified some things are, you can make "Certified UNIX" out of MS-DOS by rewriting the userspace tools and writing libc with "POSIX-ly correct" syscall names.