Some suggestions

I am a keyboarder in a band and I use a three Midi keyboards setup for live playing sounds generated in a computer ( see -> https://forum.cockos.com/showthread.php?t=213568#5 ). I mostly play sampled or physically modeled sounds including the fabulous wind and brass instruments by Sample Modeling and Audio Modeling.
So of course I did some investigation on pipe organ technology and computer generated pipe organ emulations.
As I am a physicist  and a programmer, I even did my own (rather limited: only a single combination of stops, only a single keyboard) Pipe organ emulation by combining several instances of Dexit and a convolution reverbs.
Hence I was delighted to find that Modart released this great sounding instrument, which I happily was able to test out using the trial version.
Regarding the considerations I already did for a long while,  I'd like to come up with some suggestions.

1) Note-on and Note-off velocity.
I found reports from Pipe Organ players that prefer a completely mechanical organ design over an electrical one, as they want to be able to modulate the tone by moving the keys slowly. My VPC 1 keyboard generates Note-on and Note-off velocity and I understand that the physical model should be able to cope with modulated rising a falling slopes of the wind pressure at the beginning and end of the tone. I suppose this will make a lot professional organ players happy (and would be hard to do with an instrument design based on samples).

2) Intermodulation
To me it's obvious that a high pitched pipe will be modulated by the air pressure fluctutions introduced by low pitched pipes playing nearby. I 'm sure that the physical model of the pipe should be able to reproduce this behavior (while it's impossible with samples). I suppose this will improve the realism of the instrument.

3) User generated stops
It should be possible to allow the user to create additional transposed stops and fine-tune them (e.g. to natural overtones) to get 5th, 7th, 11th, 13th harmonics that are not yet provided at all, and to create any harmonics playing in dedicated sounds and possible (de-) tunings.

4) Free Mixture stops
It should be possible to allow the user to create mixture stops of any available Pipes (e.g. see "3").

-Michael