Hitoffsets in score data
currently score data contains
maxCombo
num300
num100
num50
numMiss
numGeki
numKatu
Which is pretty limited info to deal with, and forces us to assume that the player breaks combo at whatever the calculated hardest parts of the map are. Having information relating to how accurately the player hit each note would allow to properly calculate performance of a play.
Hitoffsets is also valuable data I believe is needed for pp development. It's currently only available in replays, which are too expensive to access and are only available in top 500 scores. With score data containing an array of hitoffsets, it would finally be possible to analyze the actual difficulty of each note across a wide spectrum of players and maps.
I imagine you would only need an array of signed 16 bit values for this (32,768 is plenty enough for hit offset).