I believe I have a better idea:
'Players are banned from using Champions in Ranked Matches unless they have used them X amount of times.'
This would stop Players from using a Champion first time in Ranked regardless of whether the Champion was recently released or here since the dawn of time.
It should be mandatory that a Player knows the basics (at minimum) before they participate in a game-mode designed for serious play.
-- 'But what about players who recently became Level 30?' --
A new player has to go through 200 - 300 matches (I'm not counting Smurfs) before they become Level 30. This gives them enough time to learn the basics of several Champions, especially when taking into account the Free Champion Rotation and the incentive to play Champions you earn through purchases or rewards.
-- 'But what about OTPs? --
An OTP should still learn the basics of several other Champions/Roles. This is so they:
- Don't screw over their Team-mates by picking an ill-fitting Champion for the Team-comp (Damage Type Heavy, Lacking a crucial Role, etc)
- Don't lock in a Champion that's strongly countered by the opponent (The enemy locks in Teemo? Better pick Nasus)
- Don't cause chaos in the Champion Selection process when they don't get the desired Role (Hi, I'm a Shaco OTP that got auto-filled into ADC. I'm either getting the Role I want or locking in Shaco and trolling my Team-mates).