Instead of a mount, it seems we’ll get a Full Transformation for our Dragonriding mount from the Aberrus raid in Patch 10.1.
Akin to the Raszageth Full Transformation which drops even in Raid Finder difficulty, the initial Patch 10.1 build brought what looks like another Full Transformation. The Season 2 Gladiator mount has been revealed, so chances are the following “mount” comes from Aberrus, the Shadowed Crucible raid.