I groaned as soon as I realized what this thread was about. On the one hand, I completely understand it — this is the most important question, perhaps the only
important question, when it comes to this band. On the other hand, we've armchair-psychologized this to death over decades, and ultimately, we're never going to have an answer. Stephen King fans can point to the exact early books of his that he doesn't remember writing because he was so coked up at the time; they can refer to him getting hit by a car to explain why his output after that took a marked turn for the worse. We don't have any concrete milestones like that for Billy. Or at least nothing he's ever discussed.
What he has
discussed, however, is meeting a shapeshifter. He says it happened twice, in fact. He's offered no details about when this happened, but I would like to propose that the first incident happened at some point in the late Adore era, where the figure seemed to scan him and imparted mysterious, arcane information to him. I further propose that the second incident happened immediately after the Machina tour ... and that the shapeshifter took over Billy's identity. The real Bill is in an intergalactic zoo, where he has been serenading creatures from a million planets with the most soul-shatteringly beautiful melodies you will never hear. Pod Person Bill's motives remain unclear, unless future events important to the creature and/or its race depend on Corgan's reputation being ruined over the course of the rest of "his" life. This may be a Bill and Ted sort of situation, I'm not sure.