Just a random thought here that popped into my mind, after too much pizza.
We know that the Cap sequel lists the name of his (assumed) main villain, right? "Captain America: The Winter Soldier."
What if there's a new naming convention for at least some of the Phase II movies? Thor is subtitled "The Dark World," we know; and conventional wisdom assumes that it's some reference to the Dark Elves, since we know Malekith will be *at least* one of the villains.
But I think people are greatly overinflating the importance of the Dark Elves in this movie. The casting call for extras seems to indicate a whole host of traditional Thor races, including (possibly, from descriptions) Fire Demons, Frost Giants, Rock Trolls and Valkyries. And now comes news that Alice Krige has a small role that seems to have her heavily made up, possibly in prosthetics. All this tends to indicate that Dark Elves are just *one* piece of the puzzle. And we know from the earliest reports about this movie that it's about Thor and Jane Foster journeying through the Nine Worlds.
Anyway, here's the thing: what if "The Dark World" subtitle doesn't have anything to do with Dark Elves? (I'm positive it doesn't. Doesn't even make sense.....the Dark Elves don't live in a "dark world," anyway.) And what if "The Dark World" is actually a naming convention similar to CA:TWS?
Thor certainly has a nemesis who would qualify as "the dark world." That is: Ego, the Living Planet.
That would explain why there hasn't been any major casting news beyond Eccleston as Malekith; certainly, you don't "cast" for a living planet.
I firmly believe that the Thor sequel is actually going to have *multiple* cosmic Thor villains, and is going to involve an actual tour de force of at least some of the Nine Realms of Norse mythology. When it's all said and done, I wouldn't be the least bit surprised to see cameos from several of Thor's biggest rivals, especially those that are most likely to be CGI constructs rather than actual actors/actresses. That could include Surtur, Ymir, The Midgard Serpent, Fenris Wolf, Ulik, Kurse, and, ultimately.....
....Ego: The Living Planet. The Dark World.