Mirror Mode
Played a blind pick game the other day where the top lane, support and bottom lane were the same for both team right down to the chosen skin. It was a lot of fun and gave us the idea for a mirror mode. Basically it would be the same champions on each team. You could do it in matchmaking by pairing 2 players and having them ban from the champions that each had available until there was only one left. Then each player would have that champion.
With the free champion rotation there would always be at least a few to pick from. Yeah, a player could get forced into playing a champ he doesn't like but that happens in ARAM. I'm thinking it would be a fun game mode for maybe april fools or valentines day (lore could be something about being sucked into a mirror while being vain or a 'soulmate is yourself' or some such nonsense)