Game mode Doom Bot Abilities on both teams
This would probably crash the servers, but I think it would just be so chaotically fun I had to bring up the idea. I'm not talking about playing with the doom bot abilities on player controlled champions, I'm sure people have already asked for that many times over, but what about having 5 doom bots on both sides of the map supporting 5 member player controlled teams, so 10 champs on both sides of Summoner's Rift?
I'd say put it on Twisted Treeline too, but I'm not that sadistic because even I realize 20 champions on that tiny map would suck.