Well...

The problem with the stone is that it's just too damn powerful to keep around for stories based around a long-term transformation - you wind up having to come up with all kinds of convoluted reasons why they can't just come up with some workaround or other to reverse the change. That's why so many stories take it out of play right off the bat. What I was kind of getting at with the bits I wrote for Agnes was introducing the possibility of other magic elements without putting the nuclear option back on the table.