It’s a generalization of async/await syntax in languages like JavaScript or Swift. I like that it provides a generalized syntax that could be used for coroutines, generators, or async/await without adding any of those specifically to the language syntactically.

One level of callback nesting in a function is totally fine, two is a bit confusing, but if you have many async things going on do you really want 10, 15, 20 levels of nesting? What to do about loops?

I certainly greatly prefer async programming with async/await languages that keep the appearance of linear function execution to stacking my callbacks and having a ton of nesting everywhere

Sounds like the new “capabilities” stuff in Scala.