These are good ideas.
I would like to use BIAB to write classical symphonies.
I used BIAB as a DAV Plugin for that from time to time.

For classical music or BigBand Music there should be at least the ability to use 16 Channels of Midi with 16 BIAB tracks.

Also there could be a timeline window like it is in usual sequencers like Cubase or Sonar.
There should be a possibility to change an every track on the timeline, if the instrument plays something or not at any bar.
Because normally an instrument in BIAB always plays during the hole song.
This is not usual in classical music and even in orchestral Bigband or MArchig Band music.
For instance in a symphony, there is normally no soloist and some instruments (maybe violins) play at a certain bar and then do not play for 8 bars maybe, because some other instrumenta (likw horn section or Timpani or even harpsichord) play something during that time.

So this would be a really good feature.

http://www.michael-frank.eu