How come Gunblade isn't getting the WotA treatment on spellvamp?

My guess is as a Hybrid item, people who bought it were already getting decent amounts of health back thanks to the Lifesteal. Adding the WotA changes on it would have been far too over the top for those champions who already build it, without expanding it's audience much..

There was a Rioter who stated someone was working on something similar for Gunblade in the form that you would heal off of ALL of your sources of damage, spells, autos, and even items, but it would get rid of Spell vamp and lifesteal. So theoretically you could heal off of Thornmail and Sunfire. They would probably have to reduce the heal to 10% of all sources of damage (before mitigation?) with 1/3 effectiveness from AOE items (like Sunfire) and spells. I don't know if it will go through as it has inherent balance issues. They would definitely make it so WotA and Gunblade couldn't stack.