Fraction War
How about a fun mode where you can choose one of the existing fractions like Zaun,Noxus,Demacia,Ioania (correct me if im wrong ) and every game you win youre choosen fraction`s getting points and the fraction with the most points is getting something in the end of a season like a nice icon (Balancing: a fraction with less players is getting more points then the fractions with a greater force of players) i think this will be a nice change to the game ( maybe you can have a special ranked game mode where you can only play the champs from the choosen fraction