+1
It actually a very interesting topic. I can only assume it is resources that are limiting this. Real tracks / Real Drums are real audio. Compared to PSR which is MIDI.
However, current arrangers (Genos, I believe) is using similar technology as BIAB (audio+midi). I wonder if you can play live these audio things in Genos live (change chords live) I am sure you can...
It might be that Genos is using much smaller files chopped up, so they are responsive to live chord input. Again, I fully support this idea, just not sure if it is possible with current code and average hardware people have at home.

My guess it is... If you already made your style selection (all real tracks + drums), in theory it could chop all phrasing and load them ALL. Which will likely require big and fast memory chip and time it will take to load this monster into memory. I guess, if it happens it could bring a good chunk of new people into PG world.