New Tank update passive idea (AOE move speed effect)

What if a tank has a passive that increases the move speed of enemy champs towards the tank, and decreases enemy move speed while moving away from the tank. (this would be similar to how Janna's passive works, but for enemy champs..) So if this tank ult's, dives into the enemy team, all that try to get away will be slowed, and all that try to get past the tank, to get on team's carries will be slowed as well. The drawback is that anyone moving to attack the tank will have their movement speed increased.