Linux maintainers are unwilling to get rust into the kernel, so some rust folks decided to start writing a new kernel with same ABI. This allows them to make new architectural decisions. An example being their “frame kernel” (something between a monolithic kernel and a microkernel).
If I may say, it’s more legible and the tooling is way better, right off the bat.
Good, this is a great way to direct that energy and help Rust mature without breaking a working OS.