Throughout the past few months, Riot has done experimentation with several new game modes -- at least one of those has been confirmed to come back at a currently undisclosed time.
One for All is a game mode that has all players playing the same champion on one team, in which each team votes by whom they want to play with some exception and the winner is decided by popularity. Other similar game modes that have been introduced in recent months include a 1v1 style map which players can queue for in the Howling Abyss as well as "Hexakill", a game mode where six players play on Summoner's Rift rather than the usual 5.
At this time, Riot hasn't disclosed a time window for bringing this game mode back. However, it is indicative of a start to Riot permanently adding new game modes given the popularity of them in their "trial" period, meaning we are likely to see more game modes in the future.
Source - Riot Games
