A change to Summoners Rift
Summoners Rift has been more or less the same for a long while now and we can see Riot's attempts at spicing it up with the alcoves and elemental dragon changes, but I don't think it's quite there yet. I think it would be cool to have some more drastic changes, so here's my idea:
Replace Rift herald with a sort of portal area. When you step inside, you are transported to a completely new map, much smaller, but still fairly large (smaller than 3v3). This could be something like a cave that when you walk inside is a sort of Ice age: Dawn of dinosaurs-esque area.
Inside there are many new species of monsters and different things. Perhaps there is a new monster objective that when someone tries taking it, the map rumbles and ferocious roars are heard to players in the summoners rift map to alert people that someone is battling. Maybe this is a good place to re-introduce Vilemaw, the giant spider, as a side objective that gives players bonus health and tankiness as the gift of Vilemaw, a play on his gift of immortality to Elise.
Another option could be a completely overgrown and abandoned forest where trees and bushes are nearly everywhere and monsters like plants and wolves will attack you if you try to enter certain areas, making it a more hostile PVE environment instead of the old "attack when attacked" monsters of the jungle.
Maybe it could be a place guarded by a gatekeeper that you have a chance to defeat for a choice of 5 buffs, you have the choice to give a buff to any one of your teammates, including yourself, but you may only choose one.
Let me know what you guys think or if you have a better suggestion.