Yes, this is the lowest layer of the story. For actually writing an app, writing something higher-level makes sense: consider the relationship between raw futures and Finagle, for example. You have to build out the lower layers before you can add the upper ones, though.

Rust doesn't natively supply anything like green threads, as they have too heavy of requirements. But there are librarys that can implement them, since Rust is so low-level: https://crates.io/crates/mioco as an example.