As a result of the Ezra Miller appearance in Crisis On Infinite Earths, we get a couple of nuggets of information regarding the upcoming Andy Muschietti-directed The Flash movie.
While explaining the cameo, Crisis On Infinite Earths showrunner Marc Guggenheim says the movie is Flashpoint and basically confirms Ezra Miller is locked into the role (note: bold my own).
I was really working hand-in-hand with Jim [Lee]. From the moment we found out that this was a possibility, to once we knew Grant Gustin was cool and on board with it and Ezra was on board with [Crisis], I would send drafts of the scene to both Jim Lee and [DC Entertainment’s film VP] Adam Schlagman and we would just go back and forth. The trick with the scene is that I didn’t want to and they didn’t want me to do anything that stepped on the toes of the Flashpoint movie that they’re developing. So, we really worked hand-in-hand. Jim was really great about just making sure that all the parties were talking to each other, that nothing was getting stalled. He was a cheerleader when he needed to be, a diplomat when he needed to be. He really stepped up in every way one could do it. His enthusiasm really helped make this possible.
Regarding Ezra Miller possibly not playing the part, there was an earlier report that said Miller was pitching his own version of The Flash movie with DC Comics writer Grant Morrison, and that if WB didn't accept the pitch, Miller was going to leave the role, but we see that obviously isn't happening.
Update: Warner Bros. also requested Crisis use Ezra Miller.
Flashpoint will be different than the comics
In the comics, Flashpoint is a darker story that sees Barry Allen go back in time to stop the murder of his mother by the Reverse Flash which wrecks havoc on the timeline and creates the alternate timeline known as Flashpoint. Among the changes includes that Bruce Wayne never went on to become Batman; instead, his father, Thomas Wayne becomes the Dark Knight after his young son, Bruce, is killed, with his wife, Martha Wayne, going crazy as a result of her son's death and she goes on to become the Joker. Flashpoint also sees Wonder Woman's Amazon's at war with Aquaman's Atlanteans, which is destroying the world, and the timeline universe of Flashpoint is without hope as baby Kal-El has been kept hidden away and experimented on by the government and never got the chance to become Superman.
It's recently become known that the DC movie will not be going the route of the comics, possibly suggesting a lighter approach than the comic book story.
In an interview, director Andy Muschietti was quick to not reveal too much only offering his take on The Flash movie will be a “different version of Flashpoint than you’re expecting.”
Muschietti also previously said not to expect a horror movie, as he directed the IT flicks.
"An element of horror? I don’t think so," Muschietti said." What captivated me about the Flash is the human drama in it. The human feelings and emotions that play in the drama [of it]. It’s going to be fun, too. I can’t promise that there will be any horror [elements in it], really, but it’s a beautiful human story.”
The Flash gets released on July 1, 2022.