The question is whether there is merit from Apple's perspective in making these APIs public.
Because often we find out at WWDC a year later why they didn't make it public and it's because of some foundational rearchitecture.
It's just that the world doesn't revolve around one particular issue. If your particular issue doesn't have lots of duplicates (i.e. common) or it isn't strategically important to Apple then it just doesn't get prioritised.
Where does it state this?
I don't know about radar. Never tried it.
Given my own experiences in the past, I would doubt that radar goes much of anywhere either. Apple just doesn't seem like they move unless and until they want to. But again, I can't say for sure about radar, as I said, I've never gone that route.
By far the best route to go is to be in a position where Apple was about to make the change you wanted anyway. But you probably have to get pretty lucky for that to happen.
Radar goes nowhere, going public does.