Every time someone brings this up, I picture this map;
I figure a desert would be the best setting. 5 lanes, completely straight from left to right, 2 towers in each lane, with an inhibitor tower at the end of each, and the nexus behind all of this.
It's a castle siege. You obviously can't stop all the lanes fully, but they'd all be rather close so you'd constantly be jumping between them across this open battlefield.
The map would have a few large rocks and boulders, and random brush nearby them or just in the open, sandstorms blowing by.
I think it'd offer some really unique laning scenarios, given that the lanes would be equal to number of players. Just a thought.