Very interesting, seems really useful for custom midi controllers.
Yeah, that's what the 32-encoder board I designed (for a client) does - a synth of some sort; I'll ask him if he's OK if I post pictures. Various knobs to change variables like frequency, wave type (sawtooth, etc)... I don't know what else, but he was asking for as many knobs as he could possibly get, haha.
As far as this board... it's not useful except to prove that the encoders work in the matrix. IDK if you watched the video (first attachment), but I've set it up so that turns on alphabetic keys shift their mapping (a -> b, b -> c on clockwise turns, and backward on counterclockwise). Really don't know what else to do with it, lol - 30 volume controls? Somebody suggested "30 volume controls but each one only controls 3.3% of the total volume" or "30-player pong somehow"...