“…comes as-is, without warranties and without any commitment for future work. Complaints will get your feature request deprioritised, may get you banned, and will look silly to any potential employer googling your name”.
Also, let’s make it a meme to call out unreasonable behaviour: stop Jigar-Kumaring!
This wouldn't be entirely without downside though, as there could be a risk that the project ends up getting steered by whoever has the most money, which may be at odds with what the broader community gets from the project. That's difficult to avoid whenever Open Source developers get paid, unfortunately. If it were limited to bug-fixes I think the risk would be slim. I'm not sure if any projects have tried this.