The term to describe reading this in 2016 when it was written in 2000 is: uncanny. So how come my tablet and cell phone aren't running Fourth/plan9?
In short, there's no money in it, which is the real takeaway from this article.
We tried the simple approach. It's a nightmare.
(Yes, on single application embedded CPUs simple is great. Those are disappearing faster than glaciers. Everything has different applications running in parallel nowadays.)
[1] The author of the article, Jeff Fox, worked for them. He died in 2011.
But if you just want it to be preemptive, you'll need a small supervisor, a heavier memory manager, and some context switches. You'll get about the same performance green threads get on modern languages.