Based on what we know so far, it sounds like the Flash, played by Ezra Miller, will be an essential component of the upcoming Justice League movie. But if recent news is any indication, the world around the Flash won't be getting nearly as fleshed out as we thought it would.
Kiersey Clemons, left, in The Only Living Boy in New York. Image: Amazon Studios
According to Batman News, we might be missing out on Iris West, played by Kiersey Clemons, entirely. They report that her scenes have been cut from the film. West, notably, is a major supporting character and love interest to the Barry Allen iteration of the Flash, with a history in the comics going back to the '50s. Her on-screen counterpart was supposed to be played by Kiersey Clemons, who seemed awfully excited about her role (she called her scenes "fucking sick"), but now we might have to wait for the Flash's standalone movie for her to make an introduction.
If this ends up being the case, it wouldn't be the first time cuts have reduced the scope of the DCEU. Jena Malone was cut from her minor role in Batman v Superman: Dawn of Justice, and as anyone who watched the (surprisingly good!) Ultimate Edition of that film can attest, entire subplots went missing when that film made the jump to focus-tested theatrical release.
Batman News is also reporting that, as of the cut of Justice League currently being tested for audiences, Jesse Eisenberg's Lex Luthor also hasn't made the cut. I'll miss you, my dear manic madman. We'll always have that weird scene with the pee.