Rustaceans at the border

To an extent you'll see that happen anyway when Rust-based modules are compiled separately from the kernel. Rust code compiled for the kernel will be specialized based on how it's used in the kernel, and the same Rust code compiled for a loadable module will be specialized for the module. In Rust that can even affect things like structure layout, unless the structure has been declared #[repr(C)].

In general this isn't a problem so long as you don't try to cross kernel/module boundaries through the (unstable) Rust ABI. The module should expose C entry points and only share #[repr(C)] data with outside code—even other code written in Rust. Even if a module happens to pull in a different version of some dependency than the kernel, the dependency will be constrained to that module and will not affect the rest of the system.