With this week's Patch 10.2.7 Dark Heart PTR build, a new datamined mount has been found, the Savage Ebony Battle Turtle!
This turtle is currently tagged as coming from a possible promotion, but it is currently unknown what promotion it'll come from. There are two other Savage Battle Turtle mounts, the Savage Blue Battle Turtle and Savage Green Battle Turtle, and both of these came from the Trading Post.
Where do you think this mount could be awarded from?