Call me when Rust becomes the interface to the most used kernel in servers and supercomputers.
On the other hand, pretty much every kernel has a C API.
My comment also isn't really a comment about rust. It's about a common misconception that the unix/linux kernel somehow talks in "C".
Libc talks in C, most of the other libraries talking for interfacing with the kernel talk in C. The kernel speaks it's own language that has no special relation to C at all.