In an interview with the Onion AV Club, Billy Corgan proves that my analysis of his full-page Chicago Tribune advertisment was correct:

[The Onion]: It sounds like you could see yourself going back with the Pumpkins.

[Billy Corgan]: No, I think the relationships with James and D'arcy are pretty poor. I haven't spoken to D'arcy in over six years. And James, I don't think I've spoken to him in almost four. So I wouldn't be counting them in on the reunion tour anytime soon.

As a result, it looks like the only member of the original Smashing Pumpkins who will return to Corgan's "reunion" will be Jimmy Chamberlin, former Pumpkins drummer. Again, Corgan:
The way we look at it is, me and him together, it's Pumpkins. We were the bulk of all the recording for the Pumpkins, except for Adore, and even trying to be in Zwan, it became almost like a farce, where other band members would be saying, "That sounds like the Pumpkins." And we'd be like "No shit." We were spending energy trying not to sound like we sound. So we've kind of just come to the conclusion, if we're going to work together, it's Pumpkins. Because that's the sound. When you hear us play together, that's the sound.

Of course, it might also have something to do with the fact that a band called "Zwan" or "Billy Corgan" would not sell as nearly as many albums as a band called the "Smashing Pumpkins."