Have you considered taking the damage cap away? I think that the lack of damage cap almost helps Kindred as a champion more than anything else. It gives her a strong purpose, and identity. She's extremely good as an objective control champion. Her ganks aren't the best, and her teamfight utility is strong, sure, with her ult and tank-shredding abilities, but I think it's really amazing how her %HP damage makes the enemy team worry about things that might not normally happen in other games. Extremely fast dragons, and very early Barons become a threat against a Kindred, so opposing players really need to keep up their ward control against her or risk losing a Baron as soon as it spawns if they play the teamfights poorly.
I think it really adds a lot to her, and I think it should stay a part of her. Capping it will severely hurt that.