The problem is that the Linux kernel is monolithic so introducing rust into it does have certain repercussions about downstream compatibility between modules.

Right now the rust code in the kernel uses c bindings for some things and there’s a not-insignificant portion of C developers who both refuse to use rust and refuse to take responsibility if the code they write breaks something in the rust bindings.

If it was pure C there would be no excuse as the standard for Linux development is that you don’t break downstream, but the current zeitgeist is that Rust being a different language means that the current C developers have no responsibility if their code refactoring now breaks the rust code.

It’s a frankly ridiculous stance to take, considering the long history of Linux being very strict on not breaking downstream code.