Iolanthe is one of my favorites, too. (Maybe my favorite, but I can never pick just one; Ruddigore and Mikado and Patience are all in there.) The one thing I've never seen done, and really want to, is an Iolanthe who is not played by the traditional middle-aged woman: i.e. one for whom the "she is only seventeen and he is five-and-twenty" sequence is actually plausible!