Ok, this is completely speculation; but based on the rumours so far, I get a feeling that the 'dragon' could be a new daemon-engine re-work of the tzeentch doomwing or firelord. Just maybe an undivied version and with the newer more awesome model designers.
Because previous the the helltalon/blade things arnt they the only other fliers chaos have had?
Also, as its such a big release, and a daemon engine- could it feature in both the Daemons codex and the Chaos one? Or different versions in each (like the Soulgrinder/Defiler- essentially the same thing just different), maybe both options in the same kit as GW are pretty keen for multi-option kits now.