This isn't just useful for high-level application logic! (If I'm catching your drift from "the compiler writes the state machines for you).

I used to write extremely low-lebel NIC firmware that was basically a big bundle of state machines. Rust wasn't ready back then but I was desperate for something like coroutines/async. I think it would have been incredibly valuable.

(There are tricks to do coroutines in C but I think they're too hacky. Also, back then we believed that RTOS threads with their own stack were too expensive, in retrospect I'm not sure we ever entirely proved that).

I may be naïve in this case but I think it would also have been super useful for the high level protocol stuff. Like: 802.11 association flows. If we could have just spun up a Tokio task for each peer, I feel the code would have been an order of magnitude smaller and simpler.