Arguably, it's going to take the popularity of Github to make this a thing. Others have tried and failed (more or less) to establish an independent, first-class product to fund software developers. Some devs are getting some play on Patreon, but Patreon is more oriented toward areas other than FOSS.

Assuming this succeeds, it will be a function of the network effect. Github has a large enough base of users to sustain this kind of project.