Last I heard, jashkenas was not a fan of adding such.
"... [P]attern matching inspired by static languages is a particularly poor fit for JavaScript (and by extension CoffeeScript), because types are extremely weak in JS." -jashkenas [1]
"[... P]attern matching is not nearly as useful in a language without rich types [...]" - jashkenas [2]
I'm on that reddit thread, respectfully disagreeing with him.