I think maybe the right answer is to have a standardized, curated group of libraries pegged at some sort of LTS release that only backports security fixes. However, someone would need to pay for creating and maintaining this -- and then you wonder where the money would come from?
That or potentially fast tracking merging popular libraries into the standard library. Or at least concepts from popular libraries. Basically all the "most downloaded" crates on the Crates.io front page should be candidates for merging into the standard library.
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.