A Silver Sable movie could still happen in the Spider-Man movie universe - which of course is now part of the Marvel Cinematic Universe. Confused yet? Here goes...
Sony Pictures still has the licences to produce films with Spider-Man... and his related characters, the same characters they had before the rights-sharing deal with Marvel Studios, which puts Spider-Man in the MCU, was struck. Before that deal, Sony Pictures had several spin-offs planned, and one of those featured the female mercenary Silver Sable. On a podcast called Meet the Movie Press, Jeff Sneider said that the project, leaked in the massive breach of Sony emails, is still alive. Screenwriter Abi Morgan (The Iron Lady, Suffragette) is reportedly in talks on the project.
This would be an interesting move for Sony as they hope that Spider-Man: Homecoming will restart their franchise opportunities in the superhero world. Silver Sable, as a spy and mercenary, could fulfill the great desire from fans clamoring for a Black Widow movie. The only issue here is, Silver Sable is an extremely unknown commodity to the general public. She's appeared on a few episodes of various Spider-Man animated series, and in a few video games, but it's safe to say the general public doesn't know who she is.
As for now, Sony Pictures has only officially announced Spider-Man: Homecoming and the Animated Spider-Man film.