Since debuting in Iron Man 2, Black Widow has become one of the Marvel Cinematic Universe's most prominent heroes. Her popularity has grown to the point where many fans have been clamoring for her to lead her own movie rather than be limited strictly to ensemble adventures, like Captain America: Civil War. Although Marvel Studios president Kevin Feige and other studio bigwigs have expressed interest in making that happen, there hasn't been any movement on that front, at least publicly. In Scarlett Johansson's case, she's is still on board to star in a Black Widow movie, but she may not wait around forever for the opportunity.
When asked by Variety about whether she's still taking about a Black Widow solo movie with Marvel, Scarlett Johansson said there have been occasional discussions, but she would prefer to do it while she's still keen on inhabiting the role. She said:
I talked to them about it often. It would have to fit in the idea of where they want to go. I'm invested in that character. Marvel is greatly invested in that character. If I did it, I'd have to do it while I still actually wanted to wear a skin-tight catsuit. I don't know how much longer that's going to be.
While Scarlett Johansson's comment doesn't sound like an ultimatum towards Marvel by any means, it is fair that she's hoping that the Black Widow movie will happen sooner rather than later. Since Iron Man 2 filmed in 2009, she's been involved with the MCU for seven years across five movies, and for now, it sounds like she still cares about Natasha Romanoff. That being said, one can only enjoy wearing that skin-tight catsuit for so long. Eventually she may want to depart from the MCU to use that time for other opportunities. So of all the secret projects Marvel has in the pipeline, maybe they should making Black Widow happen while the actress is still willing.
Since Phase Three is already plotted out, the soonest a Black Widow movie could be released would be at the start of Phase Four, i.e. around late 2019 or early 2020. At least Black Widow fans can take comfort knowing there isn't a shortage of direction the heroine's movie could go. It could follow her on the fun following the events of Captain America: Civil War, or it could delve back into the past to detail her early days as a covert Russian assassin. Whatever the plot is, Johansson noted in the interview that the movie would need to "have its own specific vibe" so it can stand out from the rest of the standalone Marvel movies.
Black Widow's next MCU appearance hasn't been officially announced yet, although it's more likely than not that like most of this franchise's major heroes, she'll appear in 2018's Avengers: Infinity War.