Zack Snyder's DC universe was set to end with a major reboot, according to Justice League storyboard artist Jay Oliva.
Snyder has been open about his now-scrapped plans for Justice League 2 and 3, explaining that, after Lois Lane's death, Superman was set to succumb to Darkseid's Anti-Life Equation – then after some time traveling from the remaining Leaguers and their allies, Batman would sacrifice himself to save Lois, and Superman would help in the fight against Darkseid in the trilogy's final installment.
Man of Steel, Batman v Superman: Dawn of Justice, and the Justice League trilogy would have comprised five films all together – which Snyder, speaking to Vanity Fair, called "a five-part trilogy".
In the Flashpoint comic book story, Barry Allen accidentally ruins the main timeline after traveling back in time to stop his mother's death. While Barry eventually manages to fix his mistake, it resets the DC comic book universe. It, therefore, makes sense a direct adaptation of the story would be an opportunity to reboot and start fresh.
The Flash movie, set for a 2022 release, is thought to take inspiration from this story, and at one point in development, it was even called Flashpoint. The film will see the return of Michael Keaton's Batman, as well as Ben Affleck's version of the vigilante, so expect the multiverse to come into play, too.
