A sequel to Suicide Squad is already in the works, currently planned for release in 2019. However, Screen Rant has revealed that Warner Bros. is also planning to expand that part of the DC film universe with Harley Quinn Vs. the Joker.
The current plan is that both Margot Robbie and Jared Leto will return as the title characters. Robbie is also set for another spin-off, Gotham City Sirens, which features a selection of Gotham’s female villains.
It appears it’s early days on the Harley Quinn vs. the Joker movie at the moment, as there’s very little info available, other than that Geoff Johns will produce the movie. It’s not even known when we might get to see the movie, although Warner/DC has announced a couple of release dates for films it hasn’t officially announced yet, so this may be one of those.