Though it has yet to be confirmed by Marvel, it sure as heck seems like a Black Widow movie is in the works. The movie apparently already has writers and a director, and Marvel Studios president Kevin Feige is committed to something…
According to Geeks WorldWide the Black Widow movie will start shooting at the end of February (the 28th) this year, 2019. Part of the push for the movie to start shooting so soon (besides "what took you so long?!") is the Marvel movie schedule's opening due to the delay of the next Guardians of the Galaxy movie after the idiotic firing of former Guardians writer/director James Gunn.
Since the movie hasn't been announced, there is no release date yet. If it is intended to replace the third Guardians of the Galaxy film's theatrical slot, they better hurry… That movie was supposed to launch in 2020.
Just announce the movie already Marvel!