The Flash's ability to time-travel played a major role in was the product of major reshoots that took the movie far off-course from his original vision. At this point, the famed Snyder Cut of the DC superhero ensemble has risen to a massive level of public prominence, with demand for its release only growing with every social media tease Snyder makes for it.
The reason the Justice League Snyder Cut has received such a widespread campaign is because there's clearly so much from the original version of the film that was either tossed aside or whittled down enough for it become forgotten in the theatrical version. Much of this has to do with Batman v Superman: Dawn of Justice, and it would've played a role in Snyder's version of Justice League.
Snyder has recently offered a glimpse at including Steppenwolf meeting a drastically different end.
Aside from the original ending of Justice League, there's also at least one time-travel component that was ultimately excised from Snyder's original plan. Specifically, the Knightmare future seen in Batman v Superman was to be revisited with Cyborg experiencing a vision of it while interfacing with the Kryptonian scout ship during Superman's resurrection.
With the demand for the Snyder Cut's release entering the mainstream, Snyder's tease of The Flash time-traveling to undo Steppenwolf's victory is just one of many factors that has fed the growing push for Warner Bros. to give it the greenlight. At the moment, the studio has not made any public plans for the Snyder Cut to be released. Nevertheless, with the campaign for Snyder's version of Justice League growing louder practically every day, some type of public comment on it from Warner Bros. will very likely become a necessity sooner rather than later.
