With Patch 10.1.5, Blizzard seems to be preparing to enable Dragonriding to be used in the Old World with the new Flight Styles mechanic and more mounts receiving Dragonriding animations.
Flight Styles in Patch 10.1
There are two new spells related to flying in Patch 10.1.5: Flight Style: Static and Flight Style: Dynamic. There seems to be a system coming along that will allow the player to choose if they want to keep the old flying or dragonriding as their flight method.