I know what you mean, I have asked many many many many times over the years years years for more tracks and nothing eventuated, I have tried so many workarounds over the years (the new RapidComposerVST is the best so far).
I think everything in Biab is built around the current amount of tracks.
They made RealBand for this purpose by adding Biab tracks to PowerTracks, this works for some users but most wanted a solid 64bit DAW, the engine behind the RealTracks in RealBand was solid but not RealBand.
So that's where the development of the BiabPlugin comes in.
That's why I have focused my energy on the BiabPlugin.
How it is now you can have 2 or more BiabPlugins in your DAW, copy chords from one to the others (allowing different chords on different instruments in another instance), you can construct a song very quickly just using a midi style and sending those midi channels out to tracks in the DAW, and changing a chord will regen in a sec or so. When you have it all how you like you can generate up the RealTracks/Drums, though having play from ram will be great.
In the BiabPlugin it should be soon added to highlight x bars and drag that section out into the DAW.
You can generate up whole track multiriffs and drag out any section of bars.
Each track can be soloed and preview along with the current tracks in the DAW before dragging in.
There are just so many possibilities with the BiabPlugin and not the limitations of Biab DAW Plug-In Mode.
I think the main design of Biab is for auto accompaniment, but yes still add bar 2 bar regen.