Say I write a Linux kernel module with Rust. Is it possible for that module to work on all kernel versions, out-of-the-box, just like the ones written in C?
Linux changes it's driver api all the time, so if a driver works with multiple versions in a row, it may not work with the version after that. This is no different with rustc. The only difference between a C and a Rust kernel module is that for a C kernel module it may be possible to use a different version of the C compiler even if officially not supported and definitively not working when eg the layout randomization GCC plugin is used, while for Rust this is not possible.