I don't know, I don't really see it as a problem. What is the difference between this and FANGco hiring the developer to specialize the product for them in-house, which is something that happens often?
Funny, I act completely opposite to this with respect to Patreon. If I see content that I enjoy is only getting minor donations I'm very likely to donate, even if Patreon sponsorship doesn't get me anything more. On the other hand, if a project has high donations I am unlikely to donate unless sponsorship gets me access to something additional, and even then I am more critical with the decision.
I think GitHub is more like the first scenario. You're already getting the content (code) regardless if you pay for support or not.
I'm curious if, in the long term, GitHub will extend this functionality to integrate benefits: faster support, pay for features, even access to repos for various tiers.