I think that it would be actually pretty simple to do. Just get abunch of sounds from various instruments and make them all in the same key so they could make a nice sound. Bind the sounds to individual keys, and then bam! Got your sound together then add singing in that is already implemented into the game if you would like. (They said karaoke will be a thing). It doesn't have to sound perfect or anything, just something fun to mess around with at least.