Awesome, Dear Boy: The whole reason this film is happening is that Margot Robbie really loves playing Harley Quinn and the DC universe and wants to bring a lot more female characters from it to the big screen.
Doing It for the Art: This movie is happening because Margot Robbie really, really wanted it to happen. She's co-funding this with her own production company, and she's gone out of her way to make it a lower budget movie starring a cast of Action Girls (a stark contrast to just about any other major franchise). She even hired a female director and screenwriter to make it.
Flip-Flop of God: The higher-ups originally stated that no DCEU movie would be R-rated, stating the the PG-13 rating would be ideal for maintaining tonal and content consistency, just like how that other franchise proceeds for its movie division. About a year later, Birds of Prey is confirmed to indeed be R-rated.
Then it was announced in late January 2019 that the film was not confirmed to be R-rated.
Since the movie is filming in LA, a lot of set videos and pics have come out from the paparazzi. One of the videos has Dinah saying the f-word (which PG-13 movies are only allowed to use once or twice). Harley is also wearing a shirt in some set pics that has it written outright◊. Meaning that it is still likely R-rated.
God Never Said That: Prior to the members of the team (Black Canary, Huntress, and Cassandra) being confirmed, there was a misconception that Harley was the main character and that she was on the team which wasnt true nor had anyone involved with the project ever said that. Margot Robbie would later confirm that Cassandra is the main character.
Laura Kinney is considered Cassandra Cain's Alternate Company Equivalent. In 2017's Logan, Laura was aged down from a teenager to an eleven-year-old played by Dafne Keen. Here Cassandra has similarly been aged down to twelve, though it remains to be seen if it's is a coincidence or not. To add another layer of similarity, the stuntwoman who performed Laura's stunts in Logan, Marissa Labog, is also doing Cassandra's stunts in this project.