New fun way to introduce new champions
I think it'd be cool if when new champions are release we the all-for-one game mode comes with it. That way it doesn't take 20 games of them getting banned or first picked, not to mention the usually play unusual position making for all 10 players gunning for them. Whats more is with the new champion there is no "right" way of playing them so it totally cool to go full AD, AP, tank, whatever so it be really fun. And a great way to experiment and learn a new champion.
UPDATE: It'd also be cool if the champions wasn't ban-able during normals, thou if they are too broken I can see this causing problems, just the same at least Riot will get a lot of feedback.