Since the PC Beta has been live, the "Leviahtan" has been found on the Inverted Spire Strike which is on Nessus. At some point, the Vex fully converted Nessus into a Machine World. The concept art seems to depict and "Vex" world being consumed:
Here is also a video of it:
From the released PS Trophy list the new Raid is called Leviathan.
Note: Look at the image in the top left corner
Note: Luke Smith wearing a shirt with the same Image on the Trophy
Note: The Collector's Edition has some more intriguing stuff in it.
Note: Concept art on the Bungie website (Eerily similar)
Destiny Grimoire alludes that the Leviathan was a massive intelligent creature that resided deep within the ocean of the gas giant Fundament long ago. It was a disciple of the Traveler and aided in imprisoning the five Worm Gods within the planet's core.
When the proto-Hive sisters Xi Ro, Sathona, and Aurash dove into Fundament's depths in search of a secret that would prevent the Syzygy, an alignment of the gas giant's fifty-two moons that would create a global tidal wave of catastrophic proportions, the Leviathan met them. Communicating with magnetic fields, it attempted to persuade them to return to the surface and follow the way of the Traveler and the Light, warning them against the seduction of the Deep, but the sisters rejected its pleas because it offered no way to end their species' suffering and avert the Syzygy.
Later, after the sisters had made a pact with the Worms, becoming the Hive and ravaging Fundament, the Leviathan tried to escape the planet's surface and take shelter with the Ammonites of Fundament's moons. The Ammonites sent their best forces to protect the Leviathan, whom they revered almost as much as the Traveler, but the Hive saw this as an opportunity.
In one fell swoop, the Hive slew the Leviathan and destroyed the Ammonite civilization, forcing the Traveler to flee for its safety. The Leviathan's corpse was fed to the Worm Gods Eir and Yul.
As for Christianity, Peter Binsfeld likewise classified Leviathan as the demon of envy, as one of the seven Princes of Hell corresponding to the seven deadly sins. Leviathan became associated with, and may originally have referred to, the visual motif of the Hellmouth, a monstrous animal into whose mouth the damned disappear at the Last Judgement, found in Anglo-Saxon art from about 800, and later all over Europe.
Cetus is a constellation. Its name refers to Cetus, a sea monster in Greek mythology, although it is often called 'the whale' today. Cetus is located in the region of the sky that contains other water-related constellations such as Aquarius, Pisces, and Eridanus.^3
Here is a picture of Cetus sideways
and a picture of the concept art
Seems too coincidental for me.
Also, Cetus is commonly used as a ship's name or figurehead denoting either a ship unafraid of the sea or a ruthless pirate ship to be feared. Cetus (and its translations) are also viewed as misfortune or bad omen by sailors. Superstitious sailors believed in a cetus as the bringer of a great storm or misfortune on the ship. They associated it with lost cargo, the presence of pirates, or being swept off course, and avoided any talk of it aboard ship.