Plan 9 is an operating system. If you're referring to goroutines, CSP is completely unrelated to any of the work done at Bell Labs. That was Hoare. Go also kept a ton of terrible ideas, like nil, void (interface{}), and default mutability.
> Go is a _systems_ language at heart.
It really bothers me when people say this, because it's just untrue regurgitation from the Go team. It's not a systems language. It's a language that's pretty good for small web services. It has expensive interop (Solomon Hykes commented on this during one of his Gotime interviews) with C (even the Go team says cgo is not Go).
> It's easy to drop into assembly for ultimate optimizations.
You can only drop down into Plan 9 assembler, which is essentially useless. Write me an SGX lib without cgo in x86 and you can make that claim.