It is going to be a pretty hard sell that mimicking pthreads is ever a good idea...
Regardless, considering the casual nature of goroutines and the deliberate heavy-weight nature of pthreads, I find it hard to see pthreads as being any sort of argument about what Go should do, regardless of pthreads' shortcomings. They are wildly different animals.
(And who the hell is using C11 like that anyway?)