I was thinking about interesting mount ideas that Zenimax could implement into the game that they haven't done, and here are some of my ideas.
1. I haven't seen the devs put in Wamasu mounts yet, and I've always loved those big electric lizards from Black Marsh
2. The Vulkesh fire lizards from High Isle would be interesting. Imagine players riding fiery lizards around Tamriel.
3. Haj-Mota variants could potentially be turned into large mounts, and maybe into 2-seaters for players.
4. Ursauk from Galen haven't been turned into mounts as far I know and should be made into mounts for sure.
5. This may be strange but the Echatere of Wrothgar could possibly be used as mounts, and even as potential two-seaters.
If anyone has more suggestions, or has any criticisms please let me know.