Thanks for your interest - although I must admit, it distresses me a bit to hear that I am 'pushing the boundaries'. I would have hoped that this concept would be well developed and mature, and that I am just using something that is readily understood and available.
Oh, don't let my comments distress you. I've been out of the game for a while. With the speed at which things are changing, if you are out of it at all; you are REALLY out of it. What you are looking to do; be very well be available.
The closest I came to what you are talking about was triggering intro, verse, chorus, bridge and endings to songs from an octapad back in the day. Some songs had breakdown sections IF needed. It actually worked pretty well, and gave us some options when playing live that a straight up track wouldn't have. Some of the crowd participation songs especially worked well with that set up; so we could extend call and response areas if need be.
Not exactly what you are looking to do though...and I get that. I will be really curious if you get it worked out. It would be awesome if you do. Sounds to me like you are really trying to have the computer act as other real players for the most part. That would be awesome!