According to The Hollywood Reporter Warner Bros and DC are developing a Harley Quinn film, with Margot Robbie to both star in and produce said feature.
Let’s be clear: DC and Warner Bros do not have a good track record with its DCCU films (of the two released this far) but we should also remember that Zack Snyder is the common denominator. Suicide Squad actually looks like it will be a good film and, if that is an indication, a film starring Harley Quinn is something for which we should all be conditionally excited.
Harley Quinn is a character that was introduced in Batman: The Animated Seriese and did not appear in the main DC canon until decades later. Suffice it to say she is a fan favorite and from the previews that have been released Margot Robbie seems to be nailing the character.