Character relations
Since the first "perma-legend" I unlocked, Warwick, I've been thinking if the allies and rivals should ever have hidden passive effects. For example, Singred is the ally of Warwick so naturally the would boost each other, say, during jungling as long as they're near each other (he's a hunter, after all). Saoka is a rival and since he's after her heart they can have a slight movement boost when near each other. If rivals should be placed on the same team, there could be effects on each other both positive and negative, depending on certain criteria.
Then again this may affect certain players in a way that might make them put down the game. Just a thought, though.