Adding a Z-Axis would be awesome!

Given half of the mobility skills wouldn't be able to go over walls unless it was an actual jump or a blink. so the adcs that could go over walls would be Corki Trist and Ezreal. Dashes wouldn't be able to go over walls like they can now. It would add an extra layer of depth to the game and would make certain picks stand out in certain comps. Though with dashes if there was no wall physically stopping you but was just a ledge like blue buff jungle to river has a dash could go over it into river but not back into the jungle. I know its probably not a feasible thing to add cause well Riot would have to actually change a ton of code and the pros would go bonkers over it and Riot would never do anything to upset them sadly...

I just think that it would add an extra layer of depth to the game and would be insanely fun to see how it changes the game!