I think MIPS RISC/Os had 'green' threads in the 80's, or I could be mixing it up with Tandem terminology, where Fiber was a constant type, I seem to recall .. either way, the idea of a userspace-managed thread scheme is as old as the hills.
The question has always been: who deals out the work, the OS or the App? and as we can see, the question will continue to be asked, and un-answered, probably ad infinitum ..
I do remember Tandem and/or Wang talking about green (transportable) threads who were okay to suspend/resume across processor units .. I wish I could find more info, but I really do recall the term being applicable way back when ..
The question has always been: who deals out the work, the OS or the App? and as we can see, the question will continue to be asked, and un-answered, probably ad infinitum ..