The fact that they haven't announced a release date yet makes me think they're still not confident about the "leaked" deadline, so they're procrastinating it as much as possible to get a week or two if needed. Releasing an expansion in December isn't unprecedented, Cataclysm, the last draconic expansion, was released on December 7, 2010.
Personally, I think this posture is problematic because we can get another rushed expansion.