New Map/Mode Concept: Free-For-All in Bandle City
With the upcoming updates to Twisted Treeline (and even Dominion), I feel there's an opportunity for one more (not one-time feature) map/mode.
Demacia/Noxus have Summoner's Rift (and Crystal Scar) which is basically their middle-ground. Freljord has Howling Abyss. Shurima had Crystal Scar for the featured Team Deathmatch (which is a great gametype that should be explored more) Shadow Isles has Twisted Treeline
While Bilgewater, Piltover, Zaun, and Ionia don't have a map/mode of their own, Bandle City will be the best fit for a 4-person Free-For-All (mainly because the place should be small enough to begin with, you know, cause of yordles).
I would also be cool with a coliseum in the heart of Noxus.