In my view, what went wrong with Unix networking 40 years ago is that it broke from the Unix model, i.e. that resources are accessed via path names, and went with binary descriptors as paths.
Agreed.
And I think somthing else where P9 differed from UNIX was dealing with OOB (control) information (i.e. ioctl(2) was a terrible misstake). Dennis and Ken created ioctl(2) with v7 as a generalization of stty/gtty from the TTY handler. At the time, it seemed like a reasonable way to handle those 'small things that need to be tweeked - like baud rate or canonicalization; but ioctl(2) quickly got abused as the universal end-around, and those things caused also sorts of issues (also being a binary interface only made it worse, although on the PDP-11 it made sense for size reasons). Creating a seperate interface from the 'file' to orchestrate/control the I/O and controlling that as a set of strings not binaries, seems like a more sane idea.