With much of Phase 4 of the Marvel Cinematic Universe shrouded in mystery at least until the arrival of Avengers: Endgame, speculation has run rampant about the films that will make up the next era of the MCU.
Possibly the most exciting film confirmed for the new phase is the standalone Black Widow movie, which will reportedly serve as a prequel tale focusing on her defection from Russia to S.H.I.E.L.D. Recent speculation suggests that the film will become the first R-rated film in the MCU, or that it has least been considered. But even if the subject was discussed, it's unlikely Disney would let Black Widow end up being rated-R.
The First Avenger
Black Widow is one of the most prolific characters in the Marvel Cinematic Universe. First introduced in Iron Man 2, she subsequently appeared in all three Avengers films and played a major role in the second and third Captain America movies. While Captain Marvel is beating her to become the first female character to headline a MCU film, and Ant-Man & The Wasp focused heavily on Janet Van Dyne, Black Widow is the most arguably the most recognizable woman in the MCU. She's a founding Avenger, a strong ally, and potentially one of the most capable heroes in the universe.
There's no way Disney is letting a character with that kind of recognition have her first solo movie be a story that children will be actively discouraged from seeing. The fact of the matter is, the MCU has never gone too dark. Even the Netflix shows (which are only really tangentially tied to the brand) never really go to the limits of the darkest material from the comics.
The universe exists, in part, because of the legion of young fans who have grown up alongside its heroes. Despite the overall lack of merchandise for the character, Black Widow is a major mainstay for the MCU, and a movie focusing on her should be a huge draw. The film has been regularly requested since Phase 2, and Disney isn't going to want to sacrifice any of the potential audience for that film by making it too violent for younger audiences.
The Winter Soldier Problem
Most of the speculation regarding the film being rated-R points to the darker potential a Black Widow movie could holds. The idea goes that Natasha's story should be darker than other Avengers tales because of her spy training and style of combat. Thus, her film could reasonably become the first MCU movie to necessitate an R-rating.
But there's really no reason to push things beyond PG-13. Captain America: The Winter Soldier is largely thought of as one of the best MCU films because of how it embraced espionage stories and genre trappings, including the violence. The film is largely a spy narrative with some very strong thoughts about real life political debates, even if the finale is about superheroes stopping a bunch of Helicarriers from killing thousands of people.
The most likely way the film could earn an R-rating would be to feature a certain level of sexuality. But on top of the fact that such an approach wouldn't gel with the overall tone of the Marvel Cinematic Universe's films, it would be completely off-brand for Disney. There's simply no way the House of Mouse is about to let a major Marvel film get hot and heavy enough to break so far away from the MCU formula that's been working for over a decade.
Directed by Cate Shortland, Black Widow is expected to released May 1, 2020.