T-500 Idea

Non-traditional harmonics schemes for the organ could be interesting. Without looking at the tone generator charts, I wonder if a square wave could be approximated in the lower register? What sort of interesting additive synthesis is possible with 88ish pitches? 

Could pitches be shifted digitally to make (nearly) arbitrary waveforms a la the Yamaha DX7? Picture a DX7 algorithm scheme with Hammond tones. There is a lot of flexibility in this potential system.

Also, don't forget using subtractive synthesis on top of the final additive signal. It would be nearly trivial to add a voltage controlled ASDR and filter section. Some of this could be closely approximated digitally as well, I'm certain that Korg or Moog filter clone source code is available. Keyboard tracking, aftertouch, and velocity sensitivity could be added as well, and each control signal could be routed (via a matrix) to any digital (or analog) parameter. 

This is getting ambitious, plenty of fun available.