Models like these existed. Flattr and Liberapay. The latter had to switch away from the pooling model because turns out when you do the pooling you essentially become a bank and that’s difficult to do legally.
Those models only work if users actually visit your website or your Github. I’m developing an app targeted at end users and I bet 90% of them have never been on Github or even know what that is.
For user-facing apps, it should always be the platform(s) distributing it that should have a pool mechanism. So google for android apps, Apple for iOS. Yeah, I know, that'll be a cold day in hell...
PC software is a tough one there since there's no one app store. Which is the PC platform's strength, but yeah, that makes a pool difficult. As you said, Liberapay tried something like this. Would be cool if something like this could become big enough to justify the legal legwork necessary for this.
So as I see it the proposed solution does remove friction to supporting a large number of projects, but doesn't solve the visibility issue very well as I expect most projects to be in that "used by something I use" category.