I don't disagree, but it seems like you're overstating your point by calling OOP "optional" in Scala (and possibly F#).

Scala is explicitly marketed as a hybrid OOP/functional language. At least from "Programming in Scala," it seems as though writing idiomatic Scala really requires both paradigms. I see Scala as adding functional programming rather than de-emphasizing OOP, the former being a common thread in new (multi-paradigm) languages.