I think one of the problems is that having one established sequence of pitches within a scale, then merely changing it semi-randomly to other pitches in the scale, then (ideally) returning to the first pattern, isn’t necessarily all that interesting. You can certainly set this sort of thing up in a sequencer like the Eloquencer—use the probability features to create a random sequence, then replicate it to another pattern, permute, then return to the stored first pattern.
More interesting variation comes from changes in root, scale and harmony. This is why I’ve been somewhat obsessed with the Sinfonion since it was first demoed. The Sinfonion promises to shift us away from explicit pitch sequencing and toward manipulating how a sequence is quantized, making the latter modulatable and playable. Hopefully, they’ll manage to get the thing built and shipped one of these days
