We need more "Quest" mechanics like what exists in Heroes of the Storm
Various heroes in Heroes of the Storm have Quest Talents where you must do something very specific to unlock a certain reward. Kel'Thuzad is a great example, in that his quest drastically increases his power once he finishes it, but he has to land skillshot-based spell combos to complete it (and all his skillshots have a wind-up).
I would love to see a Quest-based passive on a future Champion or two, and maybe even change Syndra's passive to be quest-related so that good and bad Syndra players can be more easily separated, and so that she can be given a bit more power budget by requiring her to be really aggressive to receive rewards, not just gain levels.