What if enemy cooldowns were visiable in a non-obtrusive way?
I think one of the most frustrating aspects of this game is all the critical information that you don't have access to unless you grind tons of games on many different champions or go to some 3rd party site between every game to update the gaps in your knowledge.
What if when a champion uses an ability, a small red X appears under their healthbar in one of 4 positions in a line: All the way left would correspond to Q, mid left to W, mid right to E and all the way right to R.
This wouldn't change the game in any way but would make it so people with less time to grind can play in an informed and strategic way (playing around cooldowns).