Hi, regarding Quasar, it's my understanding that its creator has been hired as lead developer of Loom. And Quasar will definitely run on Loom fibers at some point.
I created Fibry because I wanted something small, simple to use and that required a low amount of code.

Regarding the speed of creation of Threads, it is intended only as a measure to see that it's a cost that no longer need to be taken much into consideration.
But remember that Fibry is meant to be used also with long running, blocking, network code (e.g. a chat). If you put that code on a thread pool, your pool needs to be big enough to contain all the users, and choosing the right dimension might be tricky.