I just worry it's going to be abused, though. E.g. I've worked with more than one Ruby code base where someone did a kind_of? check and threw exceptions if it didn't get what it wanted even though the actual type required was anything that implemented a given method in a reasonable way for no good reason.
I hope people keep the type annotations sparse, and allow the tools to infer it unless they're prepared to link long and hard about the minimal restrictions that are reasonable.
