Yes and no. It's true that there's some portion of the kernel space code that can't be written provably safely. But there's good reason to believe that a lot of it can and that belief is what's driving this integration.

Whether Rust in the kernel succeeds or not will likely be determined by whether or not a sufficiently clear boundary can be drawn between the bit that must be unsafe (in the Rust sense) and the rest. And how much code is in the latter. I don't think we know the answer yet but some knowledgable people are willing to run the experiment on the basis that the probability seems quite high that a safe subset can be determined.

Sure but if everything you're doing can be done from userspace, then you should probably be in userspace.

In the LLM case mentioned, having to hop a syscall every few teraflops is probably not a compelling reason to live in kernel space.