The specifics of the mounts, such as skill and materials, isn't finalized yet, but we really want to get this mount/machine/gizmo into the game for engineers to enjoy. Whether it is easy or a challenge, the road to it will begin in 2.3, keep an eye out for when it hits the PTRs. ;-)
This news is so cool, makes me want to go out and level up engineering. But the question now is: what form will this mechanized flying mount take? WoW Wiki has an entry on gnomish flying machines from Warcraft 2 and their evolution into dwarven gyrocoptors and then gnomish biplanes.
But where's the line between fantasy and science fiction in Azeroth? Is Engineering just another kind of "magic"? What form would you like to see the engineered flying mount?