I know I've already made a few posts about this, but I can help but try to develop the idea with every passing update. The idea of a Forge mode allowing players to make their own custom game modes and maps would allow Riot to give players the chance to bring back modes that will no longer be continued and enjoy them. And now with TFT being released in 9.13, I feel like League has all the assets for creating a plethora of maps and game modes with the assets already available. Here's just one off the top of my head:
League of Pokemon:
With the addition of TFT I feel like this would be a perfectly easy concept for players to make with Riot's resources. Imagine being able to limit the team size in the custom game mode option for Forge to allow only one champion. Then allow for bush placement that secretly hides portals to different islands. Once a player goes through, they will have to fight an npc champion whom upon defeating they get a copy of that champion added to their roster.
I don't feel I need to continue to elaborate on the possibilities. Think of being able to make races and varying objectives.
Technically Riot even has the lore for this with Ornn, as he created Howling Abyss and could teach your PC in Forge mode: your little legend.
I don't know what do you guys think?