According to an anonymous source, Marvel / Disney is looking to make short, ten minute films that could run before big Marvel movies and would introduce characters like Doctor Strange, Black Panther, Luke Cage, and so on. They think it would be an effective way to put them on audience's radar, without wasting a lot of money and jamming them like so much exposition in Iron Man 3 or The Avengers. Right now, this is strictly rumor and whisper, and there's no solid plan as to what Marvel movie they would appear before or what characters would be introduced.
I actually think this is a great idea. It would like the post-credits sequences without requiring the insider baseball knowledge that they'll be there. (Remember, this is how audiences first met Nick Fury and Thor -- or at least Mjolnir.) They could even run on YouTube and fuel audience fervor until they run out and buy a comic book or three. It's a far better plan than making a big (or small) origin story, and watching it crash and burn when no one cares who Black Panther is.