When I said I'd already thought of it, I was referring to the general observation that n-sphere volumes support tau, not pi. You can find my original comments,

When I said I'd already thought of it, I was referring to the general observation that n-sphere volumes support tau, not pi. You can find my original comments, dating from July 2010, at http://forums.xkcd.com/viewtopic.php?f=17&t=61958 http://forums.xkcd.com/viewtopic.php?f=17&t=61958. The "epiphany" refers to the specific realization that there are three families of constants, and in particular that pi is not a member of the family of volume constants but rather is part of a useless family of its own. In any case, you certainly deserve mention, so I've added you to the acknowledgments. Thanks!