I've used Plan 9 a few times in the last handful of years.
Someone got a reasonably good Linux emulator working enough to run Firefox. What more could you need? (ok it was fairly limited in some ways, but shoot once you have a web browser, most of the rest is cake... especially if it's Chrome, because then you can install Mosh inside it!)
Not sure if that's practical on Plan 9 right now.
Is there all that much of a difference between the kind of "secondary syscall ABI" approaches that allow OSes like Windows and Illumos to virtualize Linux binaries, and autoconf-based porting of those projects so they compile for the target OS, if they only use POSIX facilities that both OSes offer the same way anyway?
I mean, I agree with you when it comes to e.g. programs that use heavy amounts of OS-specific concurrency or IPC primitives. Postgres in WSL on Windows does not have the same concurrency semantics as MSSQL on Windows does, because Postgres is using POSIX concurrency primitives and MSSQL is using NT concurrency primitives.
But if there's a subset of your kernel's syscall ABI, that already has those same semantics, and really can just be 1:1 mapped with maybe a few extra instructions to handle different argument passing conventions—then does porting such a program to the OS really achieve anything?
It would be nice if Plan 9 had vim or emacs.
Furthermore there exists "A Posix Emulator" (ape) that is serviceable.
Or maybe it just shows my bias for IDEs. :)
Maybe this will reignite interest in the platform? Maybe somebody will go ahead to port it to 64 bit ARM so it can be tried on the latest Raspberry Pi? (Yes I know the 32 bit version exists and works, but...)