Dynamic linking is one thing I miss from Swift - I used dynamic linking for hot code reloading for several applications, which resulted in super fast and useful development loops. Given Rust's sometimes long compile times, this is something which would be welcome.

There are crates for hot reloading in Rust, and they use dynamic linking.

Do you have to stick to a C-FFI like interface, or can they handle rust-native features like closures and traits?

Some stick to C FFI, some enforce that the Rust compiler version is the same which makes ABI issues irrelevant.