If it’s similar to the kernel policy, they can incorporate desirable crates in-tree if needed. A crate is just a modular unit after all. And what’s more relevant here is std/no-std dependency assumptions. References about external crates usually mean avoiding “crates.io” in the build process, not avoiding crates themselves as modular units. And even if a crate is not fully incorporated, modules from it can be copied (and possibly modified) still, as people in the real world tend to not re-implement stuff from first principles 😉