Robbie got better reviews as Harley Quinn than Suicide Squad did as a whole, so it may be a good idea to give her a movie away from the team she was part of last summer. Alongside Quinn, THR suggest the film will include ‘Catwoman, Batman’s sometime love interest; and Poison Ivy, who uses plants and their toxins to get what she wants’. Batgirl and Birds of Prey have also been rumoured.
At the moment, it’s not known when we might see Gotham City Sirens. Warner is also said to be working on a proper Suicide Squad sequel (despite mixed reviews, the first film made $750 million worldwide suggesting an appetite for another movie), as well as considering a film built around Will Smith’s Deadshot. At the moment Sirens is likely to come first, but that may change.