I don't think it's all about store items. There's a big chunk about a new world. True, they could sell it the same way as BB, in anticipation for a magicky EP maybe. But it seems to me to be all about the new feel of a place, what new skills to introduce (and you don't get this in the store), etc. Maybe they will make a new world like BB as a hint of what the next EP will be.
I believe just magic isn't enough to make an expansion pack out of. Since programming a magic skill isn't too complicated, (there are TS3 mods that include magic. *Sorry I know discussing mods isn't allowed, but I was just proving a point.). They could create a magic set with furniture and possible a town, and sell it for $15. The set wouldn't require as many man hours as an expansion pack, and it would sell like crazy.
If EA did make a Magic expansion pack, it would most likely be similar to Sim 1, Making Magic, with a magic vacation world and what not. (One thing I loved about Making Magic, was the pet dragons! I remember making them a huge garden of flowers, to eat!
) EA might even just include magic in an expansion pack, like Sims 2, Apartment living.