This is very promising news indeed!
I agree that Marvel has a full plate right now, with The Avengers and the tie-in franchises, but this actually opens a LOT of doors.
I agree with some of the users on here that a character like The Punisher might work better on TV, but it would have to be on a cable channel (Punisher has no business on network television) which presents its own issues. Even then, I think a premium channel, like HBO or Showtime, would be the ideal place for the character.
While I do want to see a Midnight Sons movie, I don't want us to jump right from Doctor Strange into an ensemble movie. Blade and Ghost Rider deserve better than to have their origins shoehorned into a team picture.
A possible blueprint and wild speculation:
Thor has, thus far, served as a bit of an introduction into the mystical side of the MCU. I agree with other fans that this opens the door for Doctor Strange, if not leads directly into it. Someone else phrased it perfectly: Let Doctor Strange serve as the anchor for the "Mystical Marvel" branch, should his movie prove a success.
Now, I know that some users here detest the idea of them ending the Iron Man movies, or The Avengers franchise, but we have to be realistic: Franchises either end while they are still good, or they continue on until they are a twisted, horrific shadow of what they once were (i.e. - pretty much every comic book movie franchise up to this point), and while The Avengers (and tie-in films) are still really good, that won't last forever.
So maybe after The Avengers franchise has run its course, we can get a Midnight Sons movie, but I just don't see that happening while there are still Avengers movies being made.