Mastry and Ranked
I just had a thought, what if the mastery system could be used as a way to prevent new people from playing ranked. Example, if you don't have a first level of mastery for at least 3 champs, no ranked for new players (older players are exempt). Or maybe require everyone to have the first level of mastery for every one of the roles you can play. That would encourage people to get good with the champs they like first, balance them out a little, and put in some kind of baseline skill level for ranked.