Revelations from Patch 6.3: Gods Revel, Lands Tremble

[Tehmon]

I wonder if we are to derive any meaning from the raid names, which are a reference to the Three Graces in Greek mythology, daughters of Zeus. Is Zeus going to appear, is he the last unnamed god? An ancient whose original name was Zeus?

Thalia would be the name of the next raid, which is ironic considering we are going to fight Thaliak in Thalia. Thalia is the goddess of festivities, so my hunch is that the last raid boss will be fighting all of the Twelve in a big tournament-like endurance round. Since the gods specifically seem to think of these mock battles as great entertainment that brings them joy, perhaps this is a possibility.

[Cassar]

I wonder if we are to derive any meaning from the raid names, which are a reference to the Three Graces in Greek mythology, daughters of Zeus. Is Zeus going to appear, is he the last unnamed god? An ancient whose original name was Zeus?

That would be awesome to me. The first thing that came to mind when I learned that the ancients had greek mythos names like Hades, Gaia, Hermes, was ask myself who could be the more famous deities like Zeus, Poseidon, Aphrodite. Having Zeus as one of the Twelve (now thirteen) would be I think the best way to introduce him as an important character, but we'll just have to wait and see.
And yes, I do think the final boss of the raid will be the watcher in his true form, whatever that may be.