Thank you.
That song idea is really cool! It sounds complicated to design and implement though.
I have a few different kits of ideas and sometimes they start to bleed into eachother..
I think having a button for singing (or perhaps playing -- Maybe they carry a mandolin or something around) music in the case of a musically inclined protagonist would be potential for immense characterization. We'd have a whole soundtrack of songs and what song they performed would be contingent on where in the game world or story progress they are. We could have rare/secret songs, as well. For example, you come across a mystical cave, and in this one location this one song is possible...
Conversely, there could be times when the character simply doesn't want to perform for whatever reason. Telling the character to do something with a button press and them reacting in the negative, I think, along with everything else would help foster an interesting relationship/tension between the user and the character.