If plan 9 had taken off I wonder if there would be peripherals with built-in 9P support.
For example, a network adapter that you can mount into /net/etherxyz over USB, PCI using a 9P connection. No driver needed, except to communicate with the bus. Also, external storage (hdd, ssd) with a built in filesystem exposed as 9P. UTF-8 file names, of course. Maybe 9P could be implemented in a SoC. Chris