The fact that Basic Auth is going to be phased out in favor of OAuth is mentioned in several places, and it is not possible right now to register an app for a "source parameter" if it uses basic auth.
However, I can't see how you can implement a sensible user experience using OAuth for native clients, in particular those in mobile platforms like the iPhone or Android. Redirecting users to enter their credentials in a mobile browser, and instructing them to "go back and open the app again" is a terrible experience. OAuth works wonders for webapps, but it really sucks for native ones. Is there an unwritten policy that says that mobile clients would get registered if you ask nicely? Or is the door for basic auth really closing forever?
