[nostrademons]

Isn't this just layering another, non-standard type system on top of the language itself? After all, a type system is no more than a tool to check the correctness of programs. (And often, document the assumptions that the programmer made.)

I don't think this is a bad thing in and of itself - I like how languages like Python, Lisp, Javascript, and Erlang have been able to layer typesystems on top without building them into the language itself. But I wouldn't exactly hold it up as an example of simplicity, particularly since in those languages the community hasn't agreed on any one type system.