It's not entirely abandoned. A few years ago Brad Fitzpatrick dropped by my desk because the latest Google Compute Engine virtualization stack rollout had broken Plan 9 on GCE. This was interfering with cutting a new Go release (the official releases ran on VMs running Plan 9). I don't remember the specific breakage, but that was the day we added Plan 9 to the stable of operating systems we run in our CI regression suite against new VM releases.
I don't know if the Go releases are still done on Plan 9, but it seems likely that's still an active use of the OS.
I don't know if the Go releases are still done on Plan 9, but it seems likely that's still an active use of the OS.