Riot should let communities pool Blue Essence to unlock game modes
Example:
1 week of One for All - 1 billion blue essence 1 week of ARURF - 1 billion blue essence
This would be a general 'pool' and anyone can contribute their blue essence - once the unlock is met, the game mode is activated the next week.
This would give the community the option to unlock the game modes they want to see and another place to dump that unused blue essence. I have no idea how much essence is actually generated a day, 1 billion is just a random guess.