As you all know people in league of legends play summoners rift more than any other map, thats why other queue's might become dead and why they aren't too interested in making new gamemodes with new maps that won't rotate since the player base will most likely not even play them.
What I'm suggesting isn't making a new "Gamemode" nor a "new" map and with "new" I'm saying that I'm not suggesting making a new map layout with different things (Even though I would love to see an arena map where its FFA). What I'm suggesting is making a few new maps where the basic layout is the same, top-jungle-mid-bot.
Now you're probably like, whats the point in having other map skins, well it's not a map skin. The thing I'm suggesting is making new maps where the inner paths change, jungle camps with different abilities or layouts, different objectives with different effects. Lets say in stead of the 5 dragon's we have make 4 new ones specific for that map with different effects like, Golden dragon: Get extra gold for minion/monster and champion kills.
Aside from this, change the bush locations or add more bushes, maybe make the lane layout a bit different with some curves in midlane. My point is, riot could be making different maps from the basic map which don't mean a totally different playstyle, these maps could have the same queue or different queue's or both, where you can either choose which of the maps you'd like to play in or if you don't mind any of them you could just join the general queue.
Why would I like to see this?, well when you see other games, players have preferences over different maps and like playing those maps due to specific locations of things, different objectives or whatever. I'd like to see this in league of legends because even if it's something small riot could have different maps to make changes to the game, not always changing the base map they have and introducing these changes to new maps where you can enjoy different playstyles but still enjoy the game you loved before as well.
TL;DR: Make new maps with similar layouts just different locations of objectives, different objectives, bushes, jungle camps or even jungle paths.