An idea to integrate more lore into the game
Upon reaching the maximum mastery level with a champion, you would unlock a short story with their "Good End".
For example:
becoming fully human
killing Thresh
finding the moonstone
becoming queen of the Freljord
avenging his master
Some of the benefits of this would be giving players more of a connection with the champions they play, encouraging players to main a champion, and making champion mastery feel more meaningful.