Just to clarify: it's not that easy. The syscalls are the first step, and then you'll need a scheduler. Once you have those two, you still need new synchronization mechanisms and APIs.
Quasar doesn't just provide lightweight threads. It has rich libraries that help you make the best of them.
I'm excited by the idea that threads are going to be "the right way", once these improvements make it out of the 'plex.
I also like that I can get a similar API today with Quasar :-)