How to correct Thornmail

I have noticed that Thornmail is not a famous defensive or strategic purchase due to the fact that other def items are more cost efficient. Rather than simply changing the price of the recipe, Thornmail could be an anti-AD or anti-assassin item by making its unique attribute an active 100% damage return form all souses in a give time period rather than 30% basic attack return.

(Simmilar to Dota 2 Blademail) Active: Damage Return - Returns any damage you take to the unit that dealt the damage. Lasts 4.5 seconds.

This could be a valid counter-item for purchase since assassins are currently picked very often.