It was recently announced Marvel/Disney secured two new release dates for untitled projects. The unknown films are slotted for May 6th 2016 and May 5th 2017. It looks we might be getting an official announcement at Comic-Con about these films. DailySuperHero is reporting on a rumor that Marvel could reveal their Doctor Strange film plans (along with casting?) at their pannel and which might fill that May 2016 slot. A while back it was reported by Twitch that the studio had been circulating a script from writers Thomas Dean Donnelly and Joshua Oppenheimer to potentinal directors. Kevin Feige all but confirmed to Collider that Strange would be among the new releases in Phase Three. Which would come after Edgar Wright's Ant-Man (the first film of Phase Three) in November 2015. A May 2016 release date sounds about right for the project. As Marvel is looking like they'll be shooting Ant-Man/Avengers 2 in 2014 after Guardians of The Galaxy wraps up leaving some room in 2015 for new a production.
ThePlaylist mentioned that there was talks the studio was looking at Joel Edgerton for the lead role of Dr. Stephen Strange. However, this was also around the same time that it was rumored the character would show up in Thor: The Dark World. Viggo Mortensen (History of Violence, Lord of The Rings, The Road, Eastern Promises) had been linked for the lead but Marvel came out to deny it. More recently Iron Man 2/Tropic Thunder writer and sometime actor Justin Theroux (Your Highness, American Psycho, Zoolander) had been linked for being in the mix as well. There had been previous rumblings that Javier Bardem (The Counselor, No Country For Old Men, Skyfall) and Benedict Cumberbatch (Hobbit, Sherlock, Atonement, Star Trek Into Darkness, War Horse) had been wanted for possible roles. Considering the pair are best known for playing solid villains it's possible they might end up being in the mix for Dormammu or Mordo.
LatinoReview, who is best known for outing villains for big blockbusters believes they know who the baddies will be. They state that the villains of Doctor Strange include Dormammu, Karl Mordo and The Giant Mindless One. It's interesting mix of two staple villains from Strange's rouges gallery. I would have expected more of the horror/occult elements to come into play but it's only the first installment. Just remember this the same site that revealed villains General Zod (Man of Steel), Thanos (Avengers) and Khan (Star Trek Into Darkness.