If I remember correctly, he wasn't too fond of them using Malekith as the villain, and the new title seems to hint towards the Dark Elves. Nothing is certain at this point though. It might as well tie in to the dark magic Odin had to conjure up to get Thor to Earth in
The Avengers. Maybe he made some kind of deal that will come back and bite him in the ass.
Either way, I'm glad they didn't just went for numbers for the sequels, like the Iron Man movies.