You would end up with very unhappy developers. Each being charged rates different from the next.
30% or any set % keeps it simple. Next year it goes down to 15%.
Point I am making is they (developers) want free. They don't want to pay anything anymore because it will save them and make them more profitable. They don't like it the way it is, which is fine to have such an opinion. But, they wouldn't have wares to sell if there was no phones to sell too.
You maybe able to discern that if you buy from a third party on your iOS or Droid device, that any issues and or support lies with the third party. Well, 99% of the rest of the world will call Apple and or Google(or phone manufacture) and scream bloody murder the moment any of those transactions go south (not in a good way). Or they get hacked, mostly when they get hacked.
The system that Google and or Apple provides is not a once you buy it, it's done solution. They didn't make enough money to pay it off and it just runs in perpetuity. Epic maybe able to do the same thing with a 12% overhead cost (that they Charge their customers). But, Apple gets down to 15%, and has to support EVERYONE ELSE. Not just Epic.
So, please, pretty please. Give this mission up. Epic and or anyone else is NOT going to win here. This is retail, everyone charges. Some items get WICKED markups. Think Jeans, or Jewelry. Just because it's digital doesn't mean it's free.