I think I see what you mean about 9p not being that special, it doesn't seem much different than if Windows decided to export every system-level API as a DCOM object, that would also get you the same kind of "the whole universe is networked" kind of deal.
How does that work? I don't know the details of any implementation, but 9p the protocol appears not to have any concept of mmap: https://9fans.github.io/plan9port/man/man9/intro.html
I think I see what you mean about 9p not being that special, it doesn't seem much different than if Windows decided to export every system-level API as a DCOM object, that would also get you the same kind of "the whole universe is networked" kind of deal.