@Riot; Can you make short lore campaigns for the champions?
The gameplay could be like Torchlight or Diablo. You "buy" a champion with IP as you do now. Then you play through a short campaign (about 30 minutes to an hour long) to learn about their lore and unlock them.
For example, Tryndamere is fighting skirmishes against the Winter's Claw but the enemy warriors are Berserkers, blind with rage, much like himself. He follows their trail and attacks their encampment to investigate. Inside, he finds Aatrox. After a short battle, Aatrox flees and you've unlocked him for regular gameplay.