Until last week, the DC Comics movies that fans had to look forward to were all set in the DC Extended Universe, which launched in 2013 with Man of Steel. That all changed with the report that Warner Bros is developing a Joker origin story, which would be the first of many movies that will tell one-off tales that don't share any connection to the DCEU. It's remarkably similar to DC's Elseworlds imprint, which published a variety of non-canon comic book stories that featured familiar characters placed in different time periods, circumstances, etc.
So far the Clown Prince of Crime's origin story is the only movie that's under this new film banner, but looking at DC Comics' library, there are a lot of stories set in alternate continuities would be excellent fits. These are the DC Comics properties we hope are selected for cinematic adaptation as part of this initiative.
What happens when the public thinks that the classic DC superheroes we know and love aren't enough anymore? That's what 1996's Kingdom Come explored. After years spent in retirement, Superman donned the cape again and brought together a new team of superheroes to help him deal with the modern generation of "superheroes" who were becoming increasingly dangerous and unstable. But that was just the start, as Superman and his allies soon came into conflict with Batman's Outsiders and the Mankind Liberation Front led by Lex Luthor. The story served as a fascinating examination on if "traditional" superheroes of yesteryear are still effective in a modern world. More than 20 years after its release, Kingdom Come remains one of DC's most popular Elseworlds tales, and it's a great way for DC to keep focus on familiar faces in a world similar to the DCEU, but also with its share of differences.
Since there's no indication that there was a team of superheroes operating during the 1940s in the DC Extended Universe, a Justice Society movie would be best suited for this new DC films banner so as not to worry about continuity. Think of it being analogous to when the JSA lived on a different Earth during the Silver Age and the New 52. While there are modern iterations of the JSA in the comics, it's better if a Justice Society movie follows the team's exploits during World War II. Captain America: The First Avenger and Wonder Woman proved how entertaining period piece superhero movies can be, and much of the JSA's appeal stems from the legacy they left when battling the Axis powers. However, if the Justice Society movie were to kick off a series, it might be cool to see members like the Jay Garrick Flash and Alan Scott Green Lantern continue their fight against the forces of evil in the present day thanks to their aging being halted.