I know that Intrepid have talked about having a very few amount of flying mounta at one time on a server, but I think a very cool thing to add would be something of a gliding mount that any player can have. Of course there would be draw backs so that not everyone is going to only use the gliders, such as lower base movement speed compared to other mounts such as with water mounts on land. But it could just be a very cool variety to add to the game. Or even have gliders just very hard to unlock but still you can just own them? Because I could only see gliders being very good in mountain type biomes after you climb to the top.
ICYMI, here is an example of a mount gliding https://twitter.com/AshesofCreation/status/1433414502926766082
This can be found on the wiki ;) https://ashesofcreation.wiki/Gliding_mounts