Cooldown increase as a debuff?

Hi guys,

I was wondering, why doesn't there yet exist a way to increase an enemy champion's ability cooldowns? It seems to me like it could be an interesting new kind of debuff, like an attack speed reduction equivalent for spellcaster-type champions. In practice, it would be somewhat similar to a silence, except that a silence disables the casting of any abilities, while cooldown rate reduction has (almost) no effect on spells that were (almost) ready to cast.

For example:

• Player A has its Q on 3s cooldown, W on 1s cooldown, E and R off cooldown.
• Player B casts a spell that reduces player A's cooldown rate by 50% for 4 seconds.
• Player A may still cast E and R.
• After 2 seconds, player A may cast W, being off cooldown.
• After 4 seconds, the debuff ends, and player A's Q still has 1 second of cooldown left.
• After 5 seconds, player A may cast Q. Its cooldown was delayed by 2 seconds.

One existing champion I could see this being applied to is Kassadin, who could have a short but heavy cooldown rate reduction added to his Q.

What are your thoughts on this? What would you suspect the impact to be on the entirety of the game?