> Crates.io and Cargo need namespaces, but the leadership flatly says no.

They are favorable to crate-name-as-namespace (so that once you have the tokio crate you can use tokio as a namespace) and there's ongoing work on that. But as said above, it takes work to implement.

There's no desire for other meaning of the word "namespace" because famously nobody ever made a well-reasoned proposal (despite the amount of social media outrage over the lack of namespace).