Capturing complex requirements in Rust helps evolution

The thing that doesn't solve though, is how much information you lose going from Rust to C. That's somewhat improving with things like counted_by, but it's a long way off.

However, even that ultimately doesn't really matter, because the barriers to calling Rust from C aren't primarily technical. It's more the attitude among some people that Rust for Linux is just a temporary blip that is bound to fail, or a hope that it does so you don't have to deal with it. Which becomes significantly harder if C code is allowed to call Rust.

There will realistically be a pretty long tail of people who need a few more years to be convinced Rust is not going away, and probably not everyone will be. However I think writing C APIs in Rust will be a lot more palatable when, say, the GPU driver you are currently using being removed seems unwelcome enough that Rust is de facto necessary anyway. But it'll be a bit until that happens.