Those rumors of Dark Elves being in Thor: The Dark World are now confirmed. Deadline has revealed that Doctor Who himself, Christopher Eccleston, has been cast as Malekith the Accursed in the sequel. As he rules over the Dark Elves of Svartalfheim, that pretty much means we’ll be seeing a whole bunch of Dark Elves in the movie.
In the comics, Malekith has had dealings with Loki and has interacted with humans; so whatever they’re doing with him in the movie it’s possible to be derived from the Walt Simonsen run of the comics. There have been rumors of Elves running around Earth underground locations (such as Subways) in the movie, so it’s possible that Malekith makes a deal with Loki to come to Earth and mess with humans, and as Earth is under Thor’s protection; that’s where the action will start.