Yeah, the classic four races and classes is a pretty good start for a basic set / beginner's box. But for the player's handbook / whatever the book you expect experienced gamers to pick up is called, you need more than that.I prefer opt-in.
But I also think the basic 4x4 model is a big mistake. Four classes and four races with everything else opt-in (i.e., spend more money before you can use it) would feel like a very impoverished, "incomplete" experience to me.