The Russo Brothers are really making a huge impact upon the Marvel Cinematic Unvierse, directing Captain America: The Winter Soldier, Captain America: Civil War, and Avengers: Infinity War. They haven’t made their post-Infinity War plans known, but they’ve hinted in an interview from China (via CBM) that they’d be interested in making solo Black Widow film.
This isn’t a for sure thing, Marvel might ask them to make another Avengers event like Secret War or a fourth Captain America film like Serpent Society. They could also break ties like Joss Whedon did after they complete these string of films. The directing siblings were very interested in Marvel’s reboot of the Spider-Man franchise, I could see them jumping onboard for sequels.
The Black Widow movie has been a seriously thing for years, with X-Men and Watchmen writer David Hayter penning a script for a solo film for Lionsgate, but was ultimately scrapped after Catwoman and Elektra bombed. There was renewed interest after Widow’s cinematic introduction in Iron Man 2, but recently it was revealed by Kevin Feige she would be relegated as a supporting player in the foreseeable future.