The question of where the previously datamined Iron Skyreaver mount comes from has now been answered. Last night, several realms experienced problems and were taken offline for several hours. When these realms came back online, there was a surprise waiting on the in-game shop in the form of a new mount, the Iron Skyreaver. Some people were able to purchase the mount before the store started giving an error message which now pops up when you try to purchase it. It's likely this was not intended to be released yet because it only appeared on realms which were affected by the downtime.
Now that the cat's out of the bag, perhaps Blizzard will bump up the original release date and make it available on all realms. If not, the select few who managed to snag one during the short window will have somewhat of an exclusive mount on their hands until it's officially released. Did you or any of your friends manage to buy one in time? Will you buy one when it is released to the store officially?
Updated: The mount has now been officially released. Hit the break for the official video from Blizzard.