In Bleeding Cool's report about the Doctor Strange directing candidates, they reveal that there's already one name floating about in regards to who might end up starring in the movie which is likely to be released in 2016 as part of Marvel's Phase 3 plans.
"According to one pretty solid Marvel-adjacent source, Arcel’s Royal Affair star Mads Mikkelsen apparently is, or has been, somewhere in the mix for the film’s early casting discussions. I’m still trying to find another source on that, or to clarify which part it would be, and whether or not Mikkelsen might have already passed or been passed over." Bear in mind that Marvel wanted Mikkelsen for the role of Malekith in Thor: The Dark World, but he was forced to drop out due to his commitments to Hannibal. That makes it likely then that Marvel still want to work with him, and a role like Baron Mordo seems even more likely than the Doctor himself. Which character do you think he's best suited to?