Well if you we can actually play in a band that would be neat. The music career is kind of bleh as it is, a lot of things could be done to improve it.
You can play in a band: the exact quote is, "Gain fame and fortune as a
member of a music band, mixologist, director, or local celebrity." (italics mine) EA can be misleading at times with their screenshots, their videos, etc; and as such anything seen or observed in those things should be taken with a grain of salt. However, when EA straight-out says that something is going to be in an expansion pack, they usually mean it. All their promises have come true with regards the vanilla game as well as all the expansion packs. (They'd sometimes say that something was going to be in TS2 and it wasn't, such as how they straight-up promised weather in the vanilla game (right down to a lightning strike in one of the teaser videos) and never delivered, but that was a completely different development team) So don't worry about that.
I, also, hope the music career gets a revamp, sort of like the medical career got for
Ambitions. I'm also anxious to see how the celebrity thing works -- is it something that's earned through sheer work and manhours, such as the star system in
TS1: Superstar? Or is it more hit-and-miss like the nectar-making system in
World Adventures? (which would also make it closer to real life, some people go decades and never make it big, whereas others produce one song or whatever and immediately hit the big time; but I think it'd also make it more frustrating)