The problem is that a Showtime pack would require the Get Famous and Moschino packs to work properly, as they dealt to some extent with showing off your talents or showing off your photography skills and that would affect a fashion shoot. It would have to concentrate on something completely different with multiple instruments, as in a band or a magician as someone said above.
Maxis said they wouldn't be doing DLC for DLC anymore but I could see them doing a fairground or showground event type of pack with bands, carousels or even a casino, as the last is allowed in a Pegi 3 pack.
Of course it could also go into a farming pack as so many farmers allow events in a couple of their fields to make ends meet these days! Instead of the huge Park lot, a lot which could be used for such events as a farmers' market, musical venue, showground - to choice, as in Eco Lifestyle. B) Just trying to get my preference in! :)