[Manishearth]

The coroutine libraries are the codegen ones, yes?

Coroutines are kinda more like a language feature that people have hacked libraries to do codegen for instead, so IMO it's pretty understandable that it needs nightly.

Many of these libraries are prototyping designs that will eventually be proposed as part of the language.

[moosingin3space]

Since Rust 1.15, most libraries that require nightly seem to be this kind of prototyping, at least to my eye.