It's really not that hyped up lately, but i really think that optional typing would be the best of both worlds in that matter. You can write your programs without thinking about types, and then you add types for safety/speed.

With a little bit of type propagation i think it would lead to quite a natural style of programming.

C#/CLR hints towards that from the other side with the dynamic type, but for syntaxic and cultural reasons, it won't be the same thing as a dynamic language allowing you to use types.

Also, Clojure type hinting is not at all optional typing, as it doesn't enforce types at all. It's purely for performance reasons, and i really think is the wrong way to go about things.