Dragon Island
This name, so far, is only represented as a piece of art in The Art of World of Warcraft, and as set of unfinished render models hidden in WoW data files. The mysterious Dragon Island was also a location in Warcraft II multiplayer maps, and was shaped like a dragon's head.
It is speculated that these might have something to do with Naga, and their capital Nazjatar - although Nazjatar is supposed to be built underwater, not on an island. However, it could as easily be speculated that they have, in fact, something to do with the Dragons (hence the name)
The Dragon Isles most significant feature are shells of monstrous sea creatures. It has also been speculated that, because of their monstrous size and resemblance to what can be found at Master's Glaive, they might have something to do with Old Gods.
The Warcraft RPG book Shadows & Light might hold a clue, one of its short stories was about a group of adventures that had plans to build a device to raise Nazjatar to the surface of the ocean. Their plan likely failed, but it begs the question on if the palace could be brought to the surface. If it could, it could very well become the island in the concept art.