I remember an interview with James Blake (I think it was on Mylarmelodies exceptional "Why We Bleep" podcast), where he talked about Mutable Instruments Yarns for some tempo detection via Midi, but it also has an arpeggiator. So my brain went to using something like the Arturia Keystep to sequence chords that can then be fed as the notes for Yarns arpeggiator, using some other sort of pulse source to step through the chords on the Keystep. It could be as in tempo or not in tempo as you'd like, and could have some interesting interactions. I think there are a few companies making Yarns clones. Just an idea! Happy patching!