Wouldn't that encourage developers to create more addictive apps, add longer UI animations, and apply other tricks to increase usage time? Valuable apps that require only short interactions would certainly suffer under this scheme.

Just letting developers get paid without taking a 30 percent cut, or not banning open source apps for including a Patreon link [1] would be a great start.

[1] https://news.ycombinator.com/item?id=21268389