Cool, you can write a 5 line echo server easier, but good luck with a high performance server handling important transactions.
(If there is documentation on how to do some of these or good example code, please point me to it, because my last attempt at getting send/rcv heartbeats efficiently didn't work.)
State machines are viable if your transition function is such that effectively every combination of (state, input) leads to a different state. If the transition function is mostly describing "go to the (single) next state or error," then you're essentially asking the user to do a lot of bookkeeping that compilers are good at and users are bad at.
Async/await really shines when the complexity arises.
In my experience, closure-based async programming is only sufficiently painless in managed languages to be worth using. When you're dealing with manual memory management (or, rather, smart pointer memory management), you spend a lot more time trying to make the captures hold onto stuff.
