The goal of the Rust-for-Linux project is to make it possible to implement kernel components in Rust and having Rust be an accepted and supported choice to do s

The goal of the Rust-for-Linux project is to make it possible to implement kernel components in Rust and having Rust be an accepted and supported choice to do so inside the upstream kernel - and for people to use that support of course. It's expected that this is primarily going to be used for driver development, at least at first, since it's quite useful there, it is something where new wholesale components are being written, and the limited compiler/platform support is acceptable. Replacing existing components, especially any core parts of the kernel, is not part of any outlined plan or roadmap.