This mode would be based on defending the nexus from waves of minions. Summoners will have to work together to stop them from destroying the nexus. It could be played on a new map or perhaps on the Twisted Treeline/Summoner's Rift. Every wave of minions would be stronger and stronger. One side of the map would be unimportant because minions would be attacking from it. This coud be a 5 to 10 men game. The jungle could be used for obtaining buffs that the whole team would get and for extra money. But these buffs would be something like a whole team blue or red buff. Also every few waves there would be a boss in one lane which would be significantly stronger than the rest of the minions. Which would make players change tactic or leave a lane to help the other players. Although since there are only two lanes in the Twisted Treeline this would not be as effective as opposing to a map with four lanes or maybe even five. But this would require a new custom map. Which would be kinda refreshing. The shop would be open only between waves unless you die during a wave. Death timers can stay the same which makes things complicated if you die late game.
All players start at the shop and have a few towers around the nexus and one tower in the lane. They would have a minute before the first wave comes and 30 seconds between every other wave.
Your nexus is destroyed or you defeat all waves. (for example 30 waves but Riot should probably decide this since it requires a lot of tweaking). For each wave that you defeat you will get a proportionally higher amount of IP points at the end.
NOTE: THIS MEANS THERE IS NO PVP, ONLY PVE
I believe that this would make every role impactful and important, and it will force teamplay in order to be successful and last longer. This mode could have levels of difficulty like the doom bots mode had. Difficulty levels could differ in the number of minions per wave or maybe with more frequent boss spawns.
This could perhaps be done even on the Summoner's Rift but I think the map is too big for this mode. IF they would actually consider making a new map for this it would be best if the nexus was in the center with four towers around it (if there would be four lanes) and one tower in each lane. So it would be logical to played by 8 summoners or 9 if they implement the jungle factor.
Also the dragon can be implemented for an optional permanent buff which would obviously differ from the Summoner's Rift buffs it gives. And maybe even Baron buff which would elapse over time. Killing the Dragon or Baron can be done between waves which requires teamplay and organization.
Please leave comments or suggest ideas if you like/don't like this.