There is an intriguing post on the official forums by Paulington that reveals some very interesting clues of what the next crown crate mounts look like, new costumes, new pets, personalities, and more.
The next crown crates appear to be “Spriggan-themed”.
Essentially, these crates are gambling with your real money to obtain crown store items no longer available or crown crate exclusives. Before gambling you might want to check your odds. An official crown crate thread has been created on the official forums.