MIDI patches as weapons is a cool idea.
[Could be expanded upon and doubled down on in having different combos of patches (3 or 4 ) representing starting classes like in some RPGS, and different branching, class-specific instruments being possible to unlock through fulfilling different class-specific or general requirements. (i.e the mathematician class can unlock an instument upon using exponentially increasing amounts of different time signatures, any class could unlock an extra instrument upon using all their instruments) the conditions for reward and rewards available could also be different than just unlocking "weapons". Different classes could do that differently as well. It could also be optional to require that the composition move respective to progression, so it would in some way linearly increase in complexity as the song went on. Sorry if this is unclear but im at work, not supposed to be staring at my phone right now, and just trying to get the thought out.]