Nah they will be scratching their butts like GNU Herd programmers are. Momentum is a bitch. It's why Windows still exists.
I think just having less in the kernel and moving bits out (like Mach) into isolated domains is probably better than reinventing the universe for some purity argument.
Windows is already shipping Rust in the kernel, with more to come. They're moving faster on this than Linux is, even with all of that historical baggage.
Remember managed C++?