Probably the reason it has not been implemented it that the tracks are currently generated into RAM as the complete track.
Maybe in the old days Biab had to do this ?
If I do the same in Reaper it is instant but is playing the track direct from disk, I can regenerate any section. Most DAW work like this. If you want Utility tracks to be the same as the BB tracks then they will have to fill up in RAM. If you generate a big song look at the RAM Biab is using, and if you want more than 255 bars how much RAM will that be ?

This is something I'm trying to get implemented with the BBPlugin so we don't have the wait times and a mountain of wav files filling up the hard drive.
The files Reaper is using are on an external USB drive playing direct from there and they are 48khz 24bit.

This can be implemented now with an option for old Pentium 100 users with XP to use the current way, but those with modern hardware will play direct from disk same as Biab plays back utility tracks direct from disk.
Once Biab calculates the sections of the source RealTrack files, instead of joining them together and writing to RAM Biab will play those sections of the wav/wma direct from disk and cut out the middle man.
This will then work as the pic below and easily regenerate any section.
As mentioned elsewhere when you freeze tracks Biab will save the RealTrack section data in the SGU then when you open that SGU the next day it will load and write them into RAM, BUT rather than do that it can play those sections direct from disk.
This will also allow frozen Biab SGU/MGU to be opened in the BB DAW Plugin with all the same sections and Utility tracks.



Biab Track Injector for Reaper
Free Biab Chord Picker Tool