It is unclear whether there is any reason for most system calls.  Plan 9
   is more unix than unix is these days.

   ioctl was good for *speed* reasons; [...]

While this may be interesting (and I've heard it all before), the fact
remains that NetBSD implements Unix interfaces, not Plan 9 interfaces.
Unless you'd care to discuss how to implement Unix interfaces on top
of Plan 9, this discussion is neither relevant nor productive, and
then I think I'd refer you to the 9-fans mailing list.