Well done, man. Seriously. Every time someone starts talking about how x language makes it "easy" to do some kind of backflip, I start peering over the fence. Then someone almost immediately implements it in a C library -- or indeed, gets there first.
But have you given any thought to the critical and urgent problem of running 10,000 Actors, 10,000 Threads, and 10,000 Spaceships?
We often forget that even though this common problem of replacing callbacks is getting more critical and urgent, people already thought about it and gave some solutions. Maybe not in higher level languages (although I think Go does a great job there). In C, I have in mind glibc's ucontext for example.
I'm trying to improve that through rinoo.
So to answer your question, if you look at the wiki section you'll see test results I've done running 20,000 Actors.
Of course, once you handle "actors" correctly (which should definitely be called fiber) you shouldn't use that many Threads (if too many you'll end up spending most CPU cycles scheduling your threads). However, rinoo handles multi-threading as well. I'm currently writing doc about it.
But have you given any thought to the critical and urgent problem of running 10,000 Actors, 10,000 Threads, and 10,000 Spaceships?