Hm, idk about rank. But I've been thinking of at least recording a player's top-scoring missions + variables (map size, mission length, extracted successfully, etc) and saving an accumulated "money" stat from total score. The reasons I'm unsure about actually implementing records that recording stuff like kills of a particular enemy might get easily deprecated if I rework or remove enemy or mission types or change how the data is recorded. So updates might break the count or just be another minor feature I have to make sure doesn't break when messing around.
Like apparently DEMO mode is broken again. xD