Indeed, they were somewhat forced to maintain their own port of Sun's JDK because Sun was in a position of power and Apple was perpetually "beleaguered" back then. In contrast, Sun had no choice but to put resources into maintaining the Windows version of the JDK. Perhaps Apple has grown to the point where they can expect Oracle to deliver the JDK on Mac if they want to have a presence there.

If not Oracle, then the OpenJDK community. Either way, if it's wanted badly enough, it will happen.

The long-shot bet would be an LLVM/VMKit implementation that is clean of Sun code.