The standalone Flash movie has reportedly been pushed back to 2021, due to star Ezra Miller's involvement with the Fantastic Beasts franchise. The DC film was expected to start production in March 2019, but the script needs more work and hence will require a delay. The as-yet untitled Fantastic Beasts 3 is scheduled to begin filming in July 2019, which means the Flash movie can't go on the floors until late 2019.
Variety brings word of the new development, with its sources claiming that Warner Bros. – which is behind both DC movies and Fantastic Beasts – has pushed back the start of filming on the Flash movie because it believes there isn't “enough time to get the script in shape” for March. Miller was introduced as the comic book character Barry Allen aka The Flash in last year's heavily-disappointing Justice League; he has a crucial supporting role in Fantastic Beasts as Credence Barebone, whose second chapter is out next month.
Several writers have worked on the script, including Joby Harold (King Arthur: Legend of the Sword), Dan Mazeau (Wrath of the Titans), novelist Seth Grahame-Smith (The Lego Batman Movie), and Chris Brancato (co-creator Narcos). The Flash already has directors in place as well, in frequent collaborators John Francis Daley and Jonathan Goldstein, who co-directed Game Night. The film bears no connection to the ongoing TV series of the same name.
While The Flash has been pushed back, Warner Bros. has a lot of DC projects on its slate. Aquaman is next up around Christmas, followed by Shazam! in April 2019, a standalone Joker movie – not part of the DC film universe – in October 2019, Wonder Woman 1984 in November 2019, Birds of Prey in February 2020, Cyborg in April 2020, and Green Lantern Corps in July 2020. There's also a standalone Batman film from Matt Reeves in the works, while James Gunn is writing Suicide Squad 2.