I do not know if this is meant for balancing purposes or not but face it which mage or AP based champion would buy?
Mostly AD based champions are the ones buying Iceborn and the AP really does not fit the item for what it is meant to be. I mean the passive is attack damage based yet it gives AP so why is that not switched to AD? We would see more of the item being bought at top lane and it may even become a major top lane item.
So why not change the 30 AP to 30 AD?