Can we have an AP-Scaling Armor item?

So basically something like this:

70 AP 20 armor 10% AS

Unique Passive: When AA'ing the same champion twice, gain 10 amor and 10% crit reduction. Aditionally, you also gain armor equal to 10% of your AP. This effect lasts for 5 seconds (25 sec cooldown).

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So basically, if a lux had 500AP and she procced the item's passive, she would gain 10(+50) Armor in total for 5 seconds. This is excluding the 20 armor she gets from the item itself.

I decided to put this in gameplay because it could help AP mages and assassins tackle adcs. Im really surprised an item like this hasnt been implimented yet. The extra armor gained based on your total AP could help avoid tankier champs like Jax from abusing it.