Well, since the Skyfire Guar mount is available Nov.30-Dec.6 I wouldn't expect to see the December Showcase until the 6th of December. Pretty sure (if I recall correctly) that they always post it on the last day for whatever is the last item for that month after 10am EST.
I could be wrong and hope I am but I'm not going to count on seeing it before next Thursday while a November Showcase item is still available.