Idea for Teambuilder...
So thinking about teambuilder, the mode is meant so that you can build a team exactly how you want it through the selection of roles for each lane. Those are tank, fighter, assassin, marksman, support and mage. While this is specific to a degree, my idea is to fully utilize teambuilder by adding certain champion restrictions as well.
Before everyone says queue times are bad enough now why on earth would we want that, listen here. It wouldn't be mandatory, and you could use it in place of a role. For example, say you want team wombo-combo. Instead of having to wait for Orianna support, Yasuo mid and Malphite top, you could simply select those certain champions for those lanes and the matchmaking would find people playing those champs.
This might slow down your queue, but it wouldn't be mandatory just like assigning a role isn't mandatory.