Pipeline, Charlie,
Thank you for investing so much time into this. Not that simple after all smile Here is what I think.
Ok... You, I, people who "knew" and folks who will read this post will get by.
However, it seems that HUGE chunk of creative content will get dismissed by most users, because it is so awkward and so buried. There are some very musically interesting items hiding in BIAB Midi styles. In my opinion, those Midi tracks (phrases) should be easily available through individual track picker with audition, same way as RT's, Rd's or loops.
If you separate BIAB into two segments, Program and Content, no matter what is user opinion on Midi styles, they are still content. It will take time for most to learn the program, but creative content should be available and accessible right out of the box, without Houdini magic.
I think the only universal solution would be a consolidated tabbed picker: One picker with separate tabs for Rt's, Rd's, Loops and Midi with their own set of filters in each tab and perhaps a general search in all. For example, type "rhumba" and it will give you related results in all tabs.

Wishlist item:
https://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=595039#Post595039