The question of safety is often much more about coding standards than actual language features. For a kernel, you'd be violating Rust's safety features left rig

The question of safety is often much more about coding standards than actual language features. For a kernel, you'd be violating Rust's safety features left right and center (or have a slow kernel that just dies on OOM; choose one) and would have to come up with your own standards for preventing coding errors in those, which is what you already have with C. To be clear, some base level of trivially safe code is certainly a nice-to-have. I just don't think the amount that helps for a kernel is that much, and the added boilerplate on more unsafe things might even obscure issues.