Can we start making items that give adaptive stats?

This would open up a whole new set of builds. Lets say an item gives 200 health 75 ap 45 ad 7% move speed Active: The last spell that was cast gets it's cd reduced by 20% for every spell including itself that is cast after this is activated. 40 second cooldown.

Stuff like this could be used by multiple champs. The creativity would be insane.