Small kassadin buff he desperately needs

Kassadins E is pretty solid early. you need to have 6 spells cast to have it activated, so it has a good balance of power and availability. But late game, when the game becomes a game of 6 spells per second in team fights, it is entirely help back by the cooldown. What i think could work, is if you are at the 6 stacks, each spell after that reduces the cd by some time. .5 seconds would be enough per spell