In my opinion the best of both worlds would just be to have Rust-style inline annotations and an "interface mode" that hides implementations (most modern IDEs c

In my opinion the best of both worlds would just be to have Rust-style inline annotations and an "interface mode" that hides implementations (most modern IDEs can already do that) and non-public function. BTW I am not sure why you would want to hide the types, I find them always useful.