There's obvious pros and cons to the developer owning that communication channel, or to a middleman owning that communication channel.
What Apple is doing here is using their total control of the application distribution channel on iOS to hold apps hostage to add an option to sell users on handing Apple control, or possibly reduce their growth by forcing them to remove the other login options.
It's mildly pro-consumer, but I think it's anywhere from mildly to very developer hostile. I'm not positive it will have a sustained effect, as developers may do what they did with Facebook and detect the proxied email and ask for the real one in its place.
And Apple may very well outlaw this practice.
Sure, Apple could add even more complexity to their review process (delaying approval), or give stiff penalties to developers for working around it.
Apple's recourse to remedy a situation where a developer does not want to allow Apple to forcefully insert itself as a middle-man is primarily punitive.
Thus, as stated, this is mildly to very developer hostile.