Products like Ketron's range, the Yamaha Tyros, and the Roland Atelier organs have had mechanisms that make for quite good (sometime scarily good) emulations of brass, guitar, sax and so forth. Some of the Roland SuperNatural stuff is making its way into more 'mainstream' products - the new Jupiter 80 has the guitar strum mechanism that sorts out inversions, strum rates and fret noise all on the fly based on what you are playing.
But I think Steve has hit the nail on the head, what most keyboard players want is fairly traditional stuff.
How many Axis 64s have you ever seen on stage?
New album 'Fantasy Bridge' available now!
Making of Fantasy Bridge Diary