I can't find the exact link now (very well might have been a video without a searchable transcript), but I recall someone asking Linus that (specifically re his previous comments on C++), and his answer was something like he saw Rust solving a problem that C genuinely does not. It's controversial, but I do think of C++, Zig, etc as solving the "same problems" as C (perhaps in a much nicer way)
His particular opinion doesn't matter if the rest of the old guard only wants C in the kernel.
A lot of pain and drama could of been prevented if he put his foot down and said only C code is allowed. Instead he left it ambiguous, and a lot of good meaning people have been damaged by this. I know I'd be upset if I had been a part of the Rust for Linux team, and when I actually wanted to get my code in I was told my contributions weren't welcomed.
I wouldn't want to mix and match languages in a project that's so vital to really the entire world. It just seems like a good way for a funky rust bug to cause billions in issues...
