Thornmail idea

I think the thing about thornmail is people don't want it to be a free damage item, and I can understand that. It's not fair to die by autoing something. To offset the damage decrease, why don't we make grievous wounds apply for a longer period of time, so that attacking the tank will now carry over negative consequences in a teamfight while allowing you to 1v1 them if you are a carry with lifesteal? As it stands the effect ends almost as soon as you stop attacking a tank and then it's like it never existed in the first place.