Ah! You see, I've always been Alliance. I've been playing since vanilla, and watched Anduin grow up basically which was incredibly adorable in its own right, but Varian's death struck a nerve with me pretty hard. I've never cried so much over a character death, except for Ysera WHICH still makes me very sad as well lol
I really like the look of your dragon, and I like the idea of him being from Haleh's brood. The Nexus is a bit iffy in terms of the Dragon Brood, so I like your suggestion, but perhaps he's posing as a Kirin Tor Mage during the fight and is working with the Alliance side. He can begin slightly before the battle, if you'd prefer, so we can playout some of the scene. I figure the only way to save Varian was for him to swoop down and snatch him before Gul'dan can get him, but no one knew he was an actual dragon.
For a while, maybe Varian lets them think he's dead, and that way our two can just work together for a while.