Masteries QOL Change
The new masteries give even more opportunities than before for game-to-game customization. It would be nice if there was a way to swap out a low-level mastery in champ select without deleting an entire tree. For example, against one team I might want slow reduction, but against another I might want AOE reduction.
One possibility would be that if you remove a prerequisite mastery, the masteries dependent on it get an X through them to show that they are turned off, until you restore the prerequisites. This might require some extra explanation for beginners, but it would make things a lot better for experienced players.