I figured out how return-as-a-value made sense only upon realizing that in the following code,

    fn funny(){
        fn f(_x: ()){}
        f(return);
    }

f() is never called because funny() returns before it gets called.

The reason you want return to be coercible to any type is so that you can write something like

    let x: i32 = if y {
        4
    } else {
        return; // type ! coerced into i32
    }

And you pick the return value of ! because return never actually produces a value that is propagated on at runtime, it immediately exits the function.

(Note this all works even with returning a value)