Doesn't Patreon fit this already?

e.g. for one random example: https://www.patreon.com/monkey2

You mean like this: https://salt.bountysource.com/

Obviously, there are also lots of open source people earning income from Patreon and the traditional bountysource too - but salt is the Bountysource clone of Patreon, specifically for OSS.

The idea is a good one. But see how none of the projects break $3k/month? And how drastically it drops down to $500? There just isn't that much money moving in that model. Period.

The Open Collective project mentioned in your sibling looks even nicer, but tops out at $5k/year.

It's not the model, it's the audience size.

These guys are making $24k per month on Patreon, for example: https://www.patreon.com/Kurzgesagt - I would guess it's just a function of their audience size and the amount of work they put into fundraising - actually asking people to contribute.

ElementaryOS have actually been working at this a little bit (unlike almost all other open source projects) - and they've built up to $1k a month on Patreon: https://www.patreon.com/elementary - plus ~$200 a month on salt/bountysource, plus direct donations, etc...

Check out Open Collective https://opencollective.com. They use the sort of model that you're describing.

This has been done to death, with Patreon being the most famous example.

The problem of this model is that it's still basically B2C, a sort of charity for free work. What we need is enabling more B2B, i.e. a flow of invoices for some nominal "premium" work.

Yes! This is basically what we've concluded at Gratipay (née Gittip). Existing crowdfunding solutions are consumer-grade, and open source needs business-grade crowdfunding, as it were. We're working on it! :)

You mean flattr?