IIRC somebody in this thread said it's not preemptive and doesn't have enough functionality. Quickly looking at it, it seems to be fully opt-in / cooperative parallelism solution which is IMO not good enough.
It's...close-ish? It could really use default non-blocking IO, but honestly the reason no one's made one integrated solution yet is that giving a callback that pushes to a channel is mostly fine. I'd like something a little more robust obviously, but it's by no means a toy.