We know that Walt Disney's (DIS -1.29%) Marvel Studios plans its films far in advance, charting out multi-year phases for its cinematic universe. And we know that the studio likes to keep things secretive until its big reveal, usually at Comic-Con. Most of all, we know it's fun to speculate about which characters will make their way to the big screen and when.

Despite having only announced releases through 2015, the studio has release dates set for unannounced films in 2016 and 2017 (and reportedly has movies planned for release through 2021). Though nothing is set until it's officially announced by the studio, recent rumors might shed some light on who we can expect to see in those unannounced films.

Paging Doctor Strange
The most recent rumors were reported by the Hollywood Reporter and indicated that Marvel is in the process of finding a director for a movie about the Sorcerer Supreme of the Marvel Universe: Doctor Strange. This isn't a big surprise -- a "Doctor Strange" film has been rumored for a while and Marvel Studios President Kevin Feige has even stated that the character "checks the box off this criteria that I have" in regard to selecting properties to make films from.

According to the Hollywood Reporter's sources, Marvel is considering four directors to bring the character to life: Mark Andrews (co-director of Disney/Pixar's Brave), Nikolaj Arcel (director of the Oscar-nominated foreign film A Royal Affair), Dean Israelite (director of the upcoming Welcome to Yesterday), and Jonathan Levine (director of Warm Bodies.)

Other rumors also have casting discussions under way, with "Hannibal" star Mads Mikkelsen being the latest rumored candidate after Johnny Depp was briefly thought to be up for the part last month.

The "Doctor Strange" comics focus on Doctor Stephen Strange, a skilled and arrogant surgeon whose hands were severely broken in a car accident. Seeking unconventional treatments, he finds himself being trained in the mystic arts and earning the title of Earth's Sorcerer Supreme. The character has already been adapted once in one of Marvel's better animated films, and it's likely that a live-action adaptation would follow at least some of the story of that release.

A possible 2016 release?
While there's no guarantee that Doctor Strange is on Marvel's production slate at all, if the rumors prove true then the film is getting closer to starting production. If Marvel Studios is getting a director and possibly a star in place, we could reasonably expect to see the character within the next few years. Since both release dates in 2015 are filled (with Avengers: Age of Ultron and Ant-Man), 2016 is the earliest that the character might reach the big screen.

The first Marvel release in any given year has historically been a major franchise, as can be seen with this year's Captain America: The Winter Soldier and 2015's Age of Ultron. The second slot typically goes to films that are untested or that the company isn't expecting to be such a blockbuster ... that's why Guardians of the Galaxy and Ant-Man are the second-string releases in their respective years. If this trend continues, then out of four possible releases in 2016 and 2017 there are only two slots for Doctor Strange.

This is where the pre-production buzz comes into play. If a "Doctor Strange" film is in the early stages of production, it's currently the only untested property that's being prepped (and should be ready in time for a 2016 release). While the "Thor" films both enjoyed the second release spot and a script has been ordered for a third film, the $639 million worldwide take of Thor: The Dark World makes it look like the "Thor" franchise might be ready for first-release status.

Is Doctor Strange really coming?
Until the film has officially been announced by Marvel Studios, it's best to treat any talk of directors and stars as little more than rumor. Nothing definitive has been said by the studio, despite many news sites taking it for granted that the film is coming out. Even a quote from Kevin Feige -- "'Doctor Strange,' which I've been talking about for years, is definitely one of them" -- is often misattributed to a discussion about the contents of Marvel's "Phase 3," when it's actually referring to characters who are under consideration for eventual adaptation. Previous projects such as The Runaways that had been talked about extensively died off before making it to production. There's no guarantee for Doctor Strange.

That said, making a film about Doctor Strange makes a lot of sense. It opens up new portions of the Marvel Universe similar to how Guardians of the Galaxy does. If Marvel intends to keep its films going into the next decade, then this sort of expansion is important because it allows the studio to appeal to fans of different genres.

Doctor Strange will also help to fill the gap left by Robert Downey Jr.'s shift away from the solo "Iron Man" franchise, giving viewers a new handsome and arrogant leading man to follow. If the rumors are true, I imagine that Doctor Strange will be announced within the next several months (possibly this summer at Comic-Con, if not before then). A 2016 release seems likely, though 2017 could be a possibility as well.

All we can do is speculate.