Mercenary System
Just an idea I had earlier. Not so much a Game Mode or Map but a new system.
So how about add some longevity and diversity to the Champion Selection, and expand League of Legends as a Game.
Features: A small line of non-ranked, map-specific, Big Risk Big Reward champions to go alongside normal champions. Let's play with some champion designs that have been held back because even though they were balanced in Twisted Treeline, they were underpowered in Summoners Rift. Or a the champion that might be too troll to allow in Ranked.
These champions would feature highly unique skills that wouldn't be suited for competitive play but offer great opportunities for strategy, fun, and experience.
Benefits: Non-competitive players can have more exciting Normal experiences. Competitive players would have a fun alternative to Ranked play. Adds longevity to champion release cycles.
Limits: Limit their selection to Team Builder and Custom Matches.
Reasoning: People already find creative ways to enhance the fun of the game. Themed "all Yordles" and "Swords" matches. The origins of ARAM. People want FUN just as much as they want balanced fair competitive play. This offers the opportunity to do things that normally would be too risky for competitive play. Open up those champions that might be too-troll for normals/ranked and put them in a place where the community can still leverage them by choice.