The 12 Step doesn't have an internal MIDI clock timing system, so it's not really feasible. It would require a significant redesign of the firmware. Not going to happen.
Plus, there are so many software arpeggiators out there, the 12 step is great at defining notes for arpeggiators. I'm not an iOS guy, so I don't have any personal suggestions, but here's a few: http://ipadloops.com/tag/ipad-arpeggiator/