Functional Skins
Imagine, for the low low (read high high) price of RP AND IP, you get a cool skin with all the trimmings and it modifies one of your skills. 4 Skins per champ, LOTS of champs. It would advertise what you were planning on doing, cuz of the skin, but you would miss out on one function of a skill for an alternate...flavor. Something that is the same, but different entirely. RP and IP so that its not pay to win but there IS a cost, heavily.