I think a Showtime pack would need to introduce something new, beyond bands, for me to get interested. I already have singers with a pianist, I wouldn't get excited to add a better system for it or adding an extra musician to the mix. I also have composers making a living from selling songs, it's a bit limited and tad boring, but they could probably not add to that without re-using content from the Get Famous pack, which would seem strange. Also, how about simmers not owning GF, should they still get the fame system in a Showtime pack, or should they just enjoy building a career without gaining any fame? Might only be fun if playing in a band is limited to hobby level, which I think would kill the idea.
Not saying the band and more could not be included, but not as a main feature. So, there would need to be something lse, bigger and newer to hit the cover of this pack :)
I'd like to see ways to bring the misc performances to our TVs. How about running a TV station? Filling it with misc performances (including bands), and the productions actually being watched in the thousand sim homes? Not only musicians and magicians, but talk shows, food shows, weather forecasts, street reports, and a lot more - and our sims could have active careers as producer or journalist/reporter/food specialist/meterologist/talkshow host etc. Could be fun... :)