How much of the code are you actually using in BBW4 (what is basically just bbw) ?
Like for a start you could put the pickers into the VST code to play demos directly through the VST.
Like I suggested having a multi picker that reads the selected database file.
Putting RealDrums generation directly in the VST should be easy enough, as this was done with Reaper.
Giving real time signatures, more chords per bar, more bars (over 255), decimal point tempos and a new save format can be added to new code in the VST a lot easier than the nightmare of changing the code in bbw.
This way you get past all the limitations of old Biab and then the VST is not waiting on Biab's slow development from the past, if at all.
Doing it this way the VST will develop a rapid pace once free of the restrictions and confines of the old Biab exe.
This way there is no pressure to redo all the old code in bbw, and long term users of Biab won't be upset as it will be independent of Biab and develop at lighting speed.

Biab Track Injector for Reaper
Free Biab Chord Picker Tool