Koramos from accursed Tower, or Fafnir. He uses a Balge model and is classed as an NPC in the files, but is not actually a dragon.
They're not ingame normally, but I thought I'd mention the bunch of skytouched dragons that have gone unused in the game entirely. (The fuffy/reptile looking ones.) Those are meshed in with the tameable dragons, but I'm not sure how workable those are. I will post pictures if I am permitted to of these.
To be cheeky, Sardok. (From Nucleus of Time) One of the hopes was to be able to tame bosses in the retail game, but they never did so for whatever reason. WoW/FFXIV lets you get copies of *some* bosses, like Deathwing, Omega, Alte Roite, so I don't think this is terribly far out, it should just be defined as a younger/different dragon from the other NPC due to being smaller. This can also be expanded into alternate colourations later down the line.
I know there's three unused dragon families too, but I know they're pretty unfinished and impossible to get in. One can dream though.