We’ve seen the BlizzCon mount in the official store collection announcement, but it looks much better in the game itself. The lightning-themed steed briefly showed up for players that purchased the pack, but it was since removed. The same happened with the two trophies from the pack.
It is unclear if the mount wasn’t supposed to be added yet or if it was removed for another reason. The store page itself does not specify a “release date” and, for comparison, the WoW mount has been in the game since the pack was available. The most likely reason is that the pack assets were not ready to be added yet, as players reported that parts of the mount trophies had placeholder art on them. Hopefully they return soon as they look amazing indeed!
You can still get the BlizzCon Collection if you’re interested over here.