Twilight Cultists have also inhabited the area, sensing the presence of the Old Gods nearby, which is explored in the questline related to Consumed by Nightmare. It is currently home of the Wildhammer dwarves and the Dragonmaw Orcs, both whom inhabited Grim Batol in the recent past. Quick edit, I forgot to mention that these eggs are very big. Twilight Highlands is a new zone in Cataclysm. TL DR? I think Deathwing and Cho'gall are mixing twilight drakes with old gods/faceless ones. Also with his nihilistic, apocalyptic, and generally "my only goal is destruction attitude," it also seems downright probable. Again, given his long history of dragon experimentation it could make sense. There's also the possibility that this is all leading up to Deathwing being eventually responsible for the infinite dragonflight (even though nozdormu was "revealed" to be the leader of the flight in wotlk, i'm still not passing judgment on that yet). the last boss will probably either be Cho'gall mutated and monstrous OR an entirely new foe, perhaps a dragon/old god hybrid leader guy (kind of like Halion is leading the twilight dragons in the ruby sanctum). Obviously there's no way to prove this just yet, but it seems to make sense, given Cho'gall's hideous transformation into an ogre/old god hybrid himself. Given the long history of Deathwing's obsession with making a perfect dragonflight (first chromatic, then blackwing/nefarian's attempt at the experiment, then nether drakes, then twilight drakes) it seems like his last crazy attempt at perfection lies with mixing dragons with his new (and technically old) friends, the old gods. What does this mean? It looks to me like Cho'gall has been mixing black dragon/twilight eggs with old gods or minions of old gods (maybe the faceless ones). it's is INSIDE the egg and slowly moving (it's blue though, of course). To achieve this effect, Blizzard reused the same model for "thorns" (the druid spell) that sticks a character's feet to the ground. Looking at these next 3 pictures, you can see that there's something "moving" inside. If you turn to the right, you can go down a little path where you'll fight the final heroic hard-mode boss of the instance: Of course, they could move the hole as an alternative, but that's not important. It's my opinion that, after you clear through the whole dungeon, you get "called back" or something to the entrance and fight Cho'gall on this spot. When you first enter the entrance, you can see a giant hole in the ground.
Upon defeating Cho'gall on heroic mode, the floor beneath you will collapse and you'll fall into a cavern of flowing lava that hides a "horrifying secret," according to Alex Afrasiabi.