You're getting pretty far away from the original claim though. Which widely used crates require nightly to take advantage of nll?

Some crates will always require nightly because there will always be some people that want to take advantage of the latest features. That's a good thing to a degree, because it encourages experimentation with said features before stabilizing them. This is completely different from implying that nightly Rust is required by a lot of popular crates, which just isn't true. Most people are productively using stable Rust.