5 mastery rank champions in ranked only
I just got this amazing idea after I just played a game which we lost just because someone was playing a champion first time.
What if you could play at ranked only champions with 5 mastery rank ? That way you won't have almost every game someone in your/or enemy team playing first time champion he has no idea how to play, against enemy who played with champion he knew how to play with.
Edit: after reading that people don't have that much champions on mastery rank 5, (and after remembering that you need 16 champions to play ranked) I think that mastery rank 1 should be enough, since you would probably have after 1-2 games at least basic level of understanding how that champion works