I stumbled upon this KickStarter program and it looks interesting that it could easily be used for the AP for most planes. Four modules can be added to the top of the keyboard allowing any combination of switches and dials. Three dials per module, or three switches per module.
Plus, you can make your own keyboard template that is displayed below the keys. You can use the touch-screen keys or the activated keys that sit on top. Your choice. Since the display is below the keys you can create your own keyboard template (colored keys!) to help guide you to the correct key. Very interesting!
Here are the links:
