Weekly Game Mode Rotation
Riot, you said you do not want to split the community between all the game modes and I agree. If a game mode has no player base because another game mode is more popular, it will die off and become a useless button in the menu.
What if you put all the limited time game modes in a rotation (like free week champions), and all under 1 category. One week it can be URF, the next week will be All-For-One, and so on. It can even be random for all I care, but bring the game modes back so we can experience it again.