Blizzard added a new proto-dragon mount in the latest Dragonflight Alpha build. It looks unique and may be tied to the Vault of the Incarnates raid.
I think the mount is tied to Mythic Raszageth, the final boss of the first Dragonflight raid as both models look very similar. Here is the boss model of Raszageth taken from the in-game Adventure Journal.
Here we have the new proto-dragon mount added in the latest Dragonflight Alpha build.