They are HERE! Many new mounts are available. Most are craftable by Bio-Engineers using Epiphany and Mutant schematics, earned through using the Incubation System.
Additionally, all mounts travel at the same speed as speeders, so you'll never get left behind.
Mounts you'll find on Tarkin's Revenge:
Bageraset, Bantha, Blistmok, Blurrg, Bol, Bolma, Bolotaur, Bordok, Borgax, Brackaset, Carrion Spat, Co-Henpa, Cu Pa, Dewback, Eopie, Falumpaset, Graul, Gronda, Gualaar, Gualama, Guf Drolg, Gulginaw, Gurnaset, Horned Dewback, Horned Raptor, Kaadu, Kai Tok, Kashyyyk Bantha, Krahbu, Kwi, Lantern Bird, Lava Flea, Mawgax, Mouf, Nerf, Painted Spat, Peko Peko, Perlek, Pugoriss, Rancor, Reek, Reptilian Flier, Ring-Nosed Reek, Sligtooth Bol, Snorbal, Spiketail Blurrg, Spined Rancor, Thune, Toxic Peko Peko, Tulrus, Tusked Bull Thune, Tybis, Varactyl, Whisper Bird.
Here's a short video showcasing every one of them!