I agree with the real women idea. Let's be honest; how hard is it to make a model look good in a promo shot? They are, after all, models. A real test of talent and product is what you can do for the average, "real life" woman.
I realize that MAC markets themselves as trendy and high-fashion, but they also market themselves as willing to take some risks. Why not change the paradigm of what people see in an ad campaign and incorporate non-models? Not for all of them, just some of them. How cool would that be?