Personally I would love variaton in tempo (and possibly meter?) of the songs! Everything is now at... 120 bpm? I feel variation would broaden the scope of difficulties. On the other hand, the tempo now works as a premise of the game. Changing that might break the flow or be difficult to program...
 "Tiny Jukebox"){kind=icon}
 "Soul Mirror"){kind=icon}
 "A Dance of Fire and Ice"){kind=icon}
 "Cuboy: Cubeture 2"){kind=icon}
 "Mitoza"){kind=icon}