This is a rhythm game and one of the best indicators of whether you are playing rhythmically is the unstable rate. Whenever I feel like I've made a good play worthy of rank it often has good UR, I think it would be neat to be rewarded for that. The amount of PP could scale with the overall rhythmic density of the map as to not overvalue PP maps, and of course, it would be only a small increase in PP. I understand that as it stands now it might be difficult to incorporate but I think it would increase the legitimacy of PP being a fair ranking system for a rhythm game.