According to The Hollywood Reporter, Margot Robbie is teaming up with Suicide Squad director David Ayer to produce Gotham City Sirens, a movie that will feature a cast of all-female DC Comics villains, with Ayer directing and Robbie reprising her role as Harley Quinn.
Gotham City Sirens was a pretty awesome comic book by Paul Dini and Guillem March that stared Catwoman, Poison Ivy, and Harley Quinn living together in a house and going on zany adventures. It was sadly canceled after only 26 issues (and several creative team changes) to make way for the DC Nu52 Reboot. It's unclear whether the movie will be based on the comic, or is just borrowing its name.
Geneva Robertson-Dworet (Tomb Raider, Sherlock Holmes 3) will write the script, with Geoff "Jeff" Johns and Jon Berg also producing.
Here's a sequence from Gotham City Sirens #9 that still makes me laugh years later: