There's another school of thought too that says the kernel has no business parsing strings with all the security implications of doing so...
yeah, it's an interesting question. But Unix is based on parsing strings. The kernel already parses lots of strings for paths, for all kinds of reasons, so adding another element in the kernel that uses paths seems acceptable.
The bigger problem for Plan 9 that started to bite was i8n. All the Plan 9 messages are English, oops. All the control messages are english. And so on.
And, further, that network architecture I referenced is much less efficient than the BSD model -- 5 system calls per accept! so that was starting to hit us here on the Akaros project, since we imported the entire Plan 9 network stack into akaros, along with the drivers. Linux left us in the dust on network connections/second. We were going to change it had Akaros continued.
ron