Variety, different feels, dynamics and being able to use your vst's and kontakt libraries 'd be grand!
To me there's a contradiction here. Here it is:
1. Users want simple.
2. Simple is General Midi.
3. Biab is therefore based on GM.
4. The midi styles are GM.
5. GM does not allow for all the dynamics and expression you're talking about.
GM is the limitation here. It's not just the basic sound quality of a high end synth vs a cheap GM synth, as you've written about it's also the nuances or expression of the midi "performance".
Creating better styles that would work well with non GM softsynths wouldn't make any difference. The reason is just because a high end softsynth is designed to respond to very subtle controls that will make a part sound much more authentic, Biab is not capable of sending those commands because they're not part of the GM spec.
This is why if you really want that level of control you can start with basic Biab style tracks but you then need to move them to a DAW where you can have that level of control over your synths.
This is not simple or fast or easy. This takes us full circle to 1 and 2 above.
If you want PG to revamp Biab to incorporate some of the new advanced midi features being talked about great, put those ideas in the Wishlist forum. Peter has surprised us before.
Bob