Good ideas are pulled into the standard library.

https://crates.io/crates/once_cell

https://doc.rust-lang.org/std/cell/struct.OnceCell.html

Not everything should be eligible for this treatment. Certainly not an HTTP library or something without extremely widespread applicability.

Nearly all of my projects used once_cell, so it's good to see that pulled in. I wouldn't want to see anyhow, thiserror, anything opinionated, or anything domain specific in the std. That's a weight you have to bear forever.

Remember how long Python 2 -> 3 took, and look at the ancient and awful stuff in Python 3's standard library. Rust is not the right language for this.