Gradual / optional type declaration, grammars as a first class language feature, async / parallel programming, rational numbers, lazy evaluation, OOP with classes and roles and an underlying metaobject protocol.
The real bummer about optional typing is that it doesn’t speed up the program. I used it all over thinking that I was “optimizing” or helping the compiler. Really I was creating more work for it.
The goal is definitely that it can enable greater optimisation and I agree that it's not a reality yet. The other benefit is that it constrains types so that you get compile time type checking, which is very useful.