Why plan9 though? The best features of it were copied by linux in one way or another. The only thing I still miss from it was that filesystem feature that let you mount other computers. I remember playing with that feature a lot, I could render a game on a different computer, because the graphics was also a file. But that's about the only unique feature I remember

Some stuff won’t build because libraries that rely on OS specific features. For this I had to remove some code that relies on POSIX system calls.