Peter,

"2. The older MIDI a styles were based on algorithms simulating a real performance, but based on patterns and rules for adopting them to different chords."

There are some very usable lines there and it seems enormous amount of them are available, but they are only selectable within the context of style they belong to, or through the "Custom MIDI" picker (which is the culprit of original request of this thread)

Of course Super MIDI is "better", I am not questioning that.
But... Having a pool, of the stems separated by instruments (style, feel, etc) derived from older MIDI styles will give users quite a bit of usable content. And as you said, it will adopt to different chords.