Look at the mount closely.
Notice the antlers and the bright shining red nose.
Now look up Rudolph The Red Nose Reindeer. When exactly does Rudolph become pivotal in the folklore?
Yeah -------> Christmas Eve would be my money bet for this mount popping on the CM.. Midnight, December 24.
And let's not forget that they DO NOT need to patch to change CM sales content anymore. The contents on the CM can now be driven by some calendar coding inside the game servers. In other words.. the fact that all the Bioware Staff will be home celebrating Christmas Eve with their families (instead of loading a midnight patch) has ZERO bearing on the Christmas Tauntaun going on sale in the CM.