I think it might be interesting, but I would suspect the resources needed to create and sustain such a game mode would be a bit much for Riot as is. They don't NEED it, so their manpower and money is better spent elsewhere.

On a different note, I have a folder of champion concepts that needs peer review. If anybody is interested, I'd love some feedback; the best ideas never happen in a vacuum, after all. You can find the folder here. All I ask is that you post constructive and specific criticism as best you can, "Your caster is bad/OP/too niche" is sort of unhelpful.