Stringing Levels together the way you want it, making pretty much an entire new game out of it in the end. And then sharing those altogether.
That's exactly what I meant by a campaign creator mode. Though I'm personally hoping it would also come with the ability to design a world map to place each level on. Like you create a world map that can be customized, but also has premade tiles or something like ghost house, and you could put your ghost house level on that, and your grass level on an area of the map that looked like grassland, or what have you.