i remember about a very old casio model(small 49 keys) having separate buttons for each accomp track, with four positions each, so you could use different drums (4 types) different bass (4 types) different two accomp tracks (4 types of course) of a style at your free will.
that was very long time ago, i think i saw this model... 17 years ago.
but more modern concept from roland it seemed quite interesting to me, but unfortunatelly was not implemented after VA series, meaning morphing style function.
i am sure something similar could be developed also for fills, or intros or endings. having degrees of combination between two fills/var/intro/endings can give almost unlimited posibilities, you'd never sound like the other owners of the same keyboard....