There are a few simple facts nobody is taking into account re: bands not integrating with the showtime singers.
1. Bands were not built to have singers. It is not as simple as "just make them work together". The bands do not play the kind of music that typically has vocalists, and the music they do play is all short, repeating sections of music. There is no way to simply add singing to this. The music doesn't sound like it should be sung to, and if it was, it'd be the same short snippet of simlish over...and over...and over.
2. Singing was not built to go with the bands. Bands play eternally, forever, until you stop them. Singing does not work this way. The performance aspect of Showtime means that sets last a limited amount of time, and sims perform limited interactions- the songs they sing will not last forever until you make them stop. It is extremely unlikely they'll work that way- it is extremely likely that they'll be specail individual songs.
3. These singers are all built around the music playing itself- they're stage performers, like on American Idol. Or they're karaoke singers. Neither of those have a thing to do with a live band.
4. The bands themselves are very much like Garage bands. They start at home, they play crappy bars, they don't ever quite get to the point where they're on stage- never, ever, at any point in time have the bands been big show famous people bands. They're all local bands. This could be changed, yes, but I'm talking *right now*. That's what they *are*.
What this means is that to integrate singing and the bands,
the entire structure of bands would have to be redone.
The bands would need entirely new music. Do you know what that means? That means various songs for each skill level of each instrument. Assuming a bare minimum of, say, 4 songs, that's 4 songs x 4 instruments x 10 skill levels, or 160 individual songs. This isn't a matter of "laziness"- 160 individual songs, even if they're not even a minute long each, is a lot. That is a LOT of time, a lot of money, a lot of planning, a lot of work. The fact that bands exist at all is impressive from this standpoint, but redoing them completely to integrate with singers is silly.
They'd have to add new animations, too- singers work in such a way that you orchestrate their performance as it goes along. You choose when they do special animations and junk like that to make the show better, you pick the next song when it's time based on audience requests, stuff like that. the band would have to do this too. The drummer would need cool flourishes and the guitar guy would likely play in crazy ways, stuff like that. And these would be independent of the singer- because remember, you're looking at a complete overhaul of the bands so they can be Showtime-style performers- singer or no singer.
And perhaps the biggest reason- Since modifying the bands to work with the singers would be an absolute necessity, this means that in order to have the complete band experience, one would need two expansion packs. Lots of people beg for cross-expansion features, but absolutely nobody wants to have to buy two packs to get one full feature. Nobody.
This is mostly speculation- but there's nothing countering any of it. If people can speculate "All they'd have to do is just DO IT", which is obviously wrong and a gross oversimplification, surely I can speculate "In order to integrate the performance-style vocalists with bands, they'd have to integrate the simple and hometown bands with the vocalists", which is at least grounded in reason. ;)
Would love it if the people on MTS saw and commented on this.