[one-more-minute]

Being explicit about side effects in the type system isn't a bad idea, but don't conflate that with blocking/non-blocking operations. Some side effects aren't async (eg console.log in JS, mutating shared state) and some pure functions are (eg GPU linear algebra operations).

Effect systems (as in Koka) are mentioned elsewhere; arguably their major innovation is being explicit about effects without sacrificing composability. Functions are only "coloured" by the type system, rather than syntactically, and can be coloured differently depending on context. This is quite different from the async/await situation.