New Game Mode idea (Permanent? Featured? Unsure)
So I got started in on MOBAs way back in Starcraft 1, and the one I remember playing the most was called Left vs Right (very original, I know). They had some mechanics which I haven't heard of making their way into any other MOBA, and I think they could work out in League as a new game mode.
One of the core mechanics was that you built new minion spawners with your champion's own gold. In essence, you had to think "Do I want this upgrade, or do I want to help get more troops on the field?". Spawners could not be placed inside your base either, and enemies could find the spawner and kill it. My best idea of how this could be implemented in League is to have a special trinket that you purchase which acts almost like a consumed Zz'rot portal (use the trinket, it places the portal and destroys the trinket). I'm assuming the minions spawned from this would have to be a bit stronger than ye average minions, but exactly what changes they'd need I'm not sure.
Another mechanic they had is that you could build defensive structures in the same manner as you could build spawners. I don't think for League these should be full blown towers, but maybe some sort of weaker tower that can be placed anywhere. Again, I think some sort of trinket would work best for these.
There were other mechanics too (you could take control of NPC vehicles to build the buildings or re-position heavy artillery), but I don't think those would really fit in with the existing minions League has.