There are no Rust bits anywhere outside drivers, and hopefully that will continue to be the case. This means that mainline Linux kernel has no hard dependency on Rust whatsoever, which also means that Rust can be excised at any point with a minimum of effort.

I'm 100% behind Christoph, the last thing Linux needs is the extra complexity that Rust brings. I'm fairly optimistic that Rust will never be a hard dependency for the foreseeable future.