Why havent we had a full blown Noxus vs Demacia or Pitlover vs Zaun? Make it similar to the VS events where you side with one faction. You can use the opportunity to make some map skins as well, i.e, a Noxus theme or Demacia theme. Dota2 has lots of these and they sell well from what Ive heard.
Im sure there are massive amounts of people that love either faction and would love an event like this, map skins have been asked for for a long time now, I dont know why cosmetics in this game are only champion based. We can have missions involving playing champions from either faction.
You can add a modified Aram where only Noxus/Pitlover champions on the red and Demacian/Zaun champions on the blue side (With which factions being used per match being randomed to keep it fair), normal Aram is kept during this duration for people who just want normal Aram.
Personally I would love an event like this