I guess it depends on what they mean by "easy". Certainly it's easier in the sense that you can just write code all day long, and not have to deal with the politics about Rust inside Linux, or deal with all the existing C interfaces, finding ways to wrap them in Rust in good, useful ways that leverage Rust's strengths but don't make it harder to evolve those C interfaces without trouble on the Rust side.

But the bulk of Linux is device drivers. You can build a kernel in Rust (like Asterinas) that can run all of a regular Linux userland without recompilation, and I imagine it's maybe not even that difficult to do so. But Asterinas only runs on x86_64 VMs right now, and won't run on real hardware. Getting to the point where it could -- especially on modern hardware -- might take years. Supporting all the architectures and various bits of hardware that Linux supports could take decades. I suppose limiting themselves to three or four architectures, and only supporting hardware made more recently could cut that down. But still, it's a daunting project.