So, recently in an interview with Total Film magazine, Marvel Studios president Kevin Feige talked a bit about Black Widow's role in Captain America: Winter Soldier and Avengers: Age of Ultron. Thanks to ComicBookMovie, portions of the interview have made it online, even if they don't know how to hotlink their source (you should still hotlink the homepage of the source even if you can't link a specific article guys).
We wanted Cap and really the entire cinematic universe to be very different at the end of Winter Solider than it is at the beginning. Therefore when we meet the Avengers at the top of Age of Ultron, it's a very different landscape than we left them at the end of the film film. Partially that's because we love the rhythm that the comic books have developed - each of the characters appear in their runs, occasionally they get together for a big event or crossover series, they part again, and then they come back together again.
[Black] Widow's part in that is very big. We learn more about her past and learn more about where she came from and how she became in that film. The notion of exploring that even further in her own film would be great, and we have some development work with that.
Now, that last sentence was too much for some to handle, with a "notion of exploration" turning into full-blown confirmation.
Granted, they go on to contradict their own title as they wrap the article, but this is how the circle jerk of rumors gets rolling. Is it something they are considering? Probably -- I'm sure they consider all types of ideas. It is confirmed? No. Is it being worked on? I highly doubt it at this time. Is it even unofficially slotted for phase three? Again, at this time, I doubt it.
UPDATE: Now MTV.com is joining the party, running the same "confirmed" story off the same quote. Stop people. Just stop.