The point of the project is not meant to be an experiment in "programming language co-development", the point of the project is to use Rust in Linux kernel development. The project was started by Linux kernel developers who want to use Rust. It's been a slow start, but as you say, it's the world's most important piece of software so progress has been careful and trying to get the foundations right before going crazy with it.

The fact that Rust gets to benefit from the project too is just an added bonus.