Can you clarify what youre referring to with "decided to implement it in the compiler instead", be it from this blog post or elsewhere?
Clearly you need coroutines in the compiler, and the way Rust treats ownership means pinning is needed in some way (I've not been following closely so don't know if this is in libstd or a language-level feature), but the rest (according to this post) seems to be going in libstd so you can write your own if you want.