We do know that Martin Scorsese is involved as producer of the recently announced Joker origin movie, with Todd Phillips slated to direct. That movie, as of now, doesn't have a Joker, with rumors hintings towards either Joaquin Phoenix or Leonardo DiCaprio.
However, what we do know is that DC and the WB are not done with "Suicide Squad," what with Margot Robbie’s Harley Quinn getting her own movie with “Birds of Prey,” and now another character, Jared Leto's The Joker, nabbing his own standalone movie.
Did we need this? Absolutely not, but I'm hoping that the WB and DCEU got their priorities straightened out, hired a great director and are working hard at making "Suicide Squad 2" work this time around. Ditto, these upcoming original movies of Harley Quinn and The Joker.
Variety has it like this:
"Warner Bros. is looking to expand on Jared Leto’s version of the Joker, which debuted in 2016’s “Suicide Squad,” with a movie of his own."
"Sources tell Variety that Leto is set to star and exec produce an untitled standalone film, paving the way for future movies branching from “Suicide Squad.”
The same source says that film should go into production sometime in 2019.