Back in the later days of the original Hammond Organ Co they offered two hi-end organs that had a unique feature: A manual arpeggiator. It was a set of contacts triggered by a row of 49 vertical tubes, located below the lower manual. You played a chord and moved a finger across the contact tubes, and the notes you held were triggered as a real time arpeggio, following your finger’s speed. The actual sounds played were called Percussion voices, having an attack, in combination with organ tones or not.
This feature could maybe be implemented with a ribbon controller converted to MIDI CC. then remapped to notes by MIDI HUB.
But how to transpose the input notes to cover notes in other octaves?
A MIDI ribbon controller can be bought complete or DIY with a sensor from SoftPot Membrane Potentiometer - 500mm - SEN-08681 - SparkFun Electronics combined with a resistance to MIDI converter from Audiofront, MIDI solutions, Doepfer etc.