I believe it was suggested by many and maybe it will by even more!
How about notes which are not wallpaper, but are like water or glue?
I suggest it, because alot peoples build amazing worlds and they want to add specific music to world, sadly they can not! Maybe someone like spaces in walls or whatever background is for, but I personally have not added single note to amazing world I owe, just because I have placed background nearly everywhere and notes would kill pretty world design...
Don't you feel like me too? Comment bellow and say your opinion about "unseen" or "water" notes!