Custom Game Revamp

I sincerely believe that there should be a revamp of custom games, with rules implemented by the host itself. Maybe even a custom game mod community that one could translate into a custom game.

That would give way to the birth of easily manageable mini games (such as Ultimate Bravery, for example) or practice with specific champions (your idea) with custom rules.
The host should have the power to, for example:
limit lives;
limit backing ability;
limit champions;
limit items;
limit where a champion can go (for example, in Catch the Teemo, the Teemo cannnot go out of the jungle);
etc.

In conclusion, Riot could offset all of that development time and leave the power to the players. This would create brand new game modes in the custom games (which is already happening), only with a much better moderated approach. See the success of simple mods like Garry's Mod, for example. The potential is huge when you factor in player involvement.

For some more ideas regarding this subject, there is also this post.