No need to make a beatbox out of BIAB. There are gazillion of loop / synth things and drum machines available within samplers/ synths like Kontakt/Komplete, Halion and many others that you can use as a plugin(s) within BIAB and feed individual midi tracks or chord track directly to these to play along with your RT's Rds and Midi arrangement.

I value BIAB specifically for traditional performances / instruments... you know the ones people actually played. I would not mind couple of more Loop Sets and Modern midi styles, sure that is a good thing.

This is in line with "wishes", but the easiest way to get "modern" Midi lines would be a simple and universal style converter from great thousands of styles (free and paid) of Yamaha / Roland / Korg to BIAB. For it to be "User Friendly" it has to be integrated.

One other item that I stressed a few days ago that in my opinion should be there in the first place, is to have ability to easily audition and pick out individual MIDI stems from PG MIDI styles. Many style instrumental parts are very usable for making modern type music, but proper workflow is simply not there yet. Hopefully that will change.