I feel Rust offers several strong points whilst actually being performant and widespread enough to be in the kernel. I doubt you absolutely _need_ to know both to work on specific parts written in either
I think Rust support should be in a more experimental branch for the kernel first before even thinking of adding it to the main code base. Mostly because I think it needs more supporting code and documentation to get people on board with such an inclusion: complexity or not.
"linux-next" is the experimental branch for the kernel.
"The linux-next tree is the holding area for patches aimed at the next kernel merge window. If you're doing bleeding edge kernel development, you may want to work from that tree rather than Linus Torvalds' mainline tree. "