> Plan 9 failed, in a sense, because Unix was simply too big and too entrenched by the time Plan 9 came around.

The Unix renaissance in the ‘90s had a lot to do with open source source OSes such as (primarily) Linux and the BSDs. Until then we had a bunch of corporate unixes, no two alike but expensive and kernel hacking was basically off limits. With the advent of i386 we had affordable & powerful computers that could run “real” OSes and us hackers were hungry for an open source OS. Computing history might’ve been different if plan9 was made open source before Linux became available. But that was not to be.