Warning - This article contains spoilers for Zack Snyder's Justice League.
For better or worse, Zack Snyder's Justice League is now out in the universe. Within its four-hour runtime is a collection of new scenes that were intended to set up Snyder's future Justice League sequels.
In particular, Snyder's cut introduced the Justice League's nemesis Darkseid, whose appearance had been heavily teased in prior films. While Darkseid didn't have much interaction with the Justice League members during the Snyder cut, the film did give a glimpse at what terrible futures the villain could cause.
During a Knightmare vision shown to Cyborg, the audience witnesses a future in which Darkseid has murdered many members of the Justice League. On top of this is a key scene where we see that Darkseid has turned Superman against his fellow heroes, leading to the evil Superman seen at the end of the film.
THE KNIGHTMARE SEQUENCE FEATURES A ROBIN EASTER EGG
The Knightmare sequence in Zack Snyder's Justice League depicts the beginnings of a post-apocalyptic world where Superman becomes a villain following the death of Lois Lane.
This is shown in the Snyder cut with a scene of Superman crying over the burned body of Lois while Darkseid stands over him.
Taking a closer look at this scene, Robin's suit can be seen in the background. As seen in Batman vs Superman, this suit is kept as a tribute to the fallen hero within the Batcave, meaning that this is also where Lois Lane's death occurs in the future.
BAD TIMES IN THE BATCAVE
The visions that both Cyborg and Batman witness during Zack Snyder's Justice League serve to set up a Knightmare future that would've been explored in Snyder's future movies. It seems Snyder intended to pull from the famous Injustice storyline, which sees the death of Lois Lane turn Superman into a murderer and tyrant on Earth.
Snyder recently revealed what his future Justice League storylines would involve, including the murder of Lois at the hands of Darkseid after Superman had asked Batman to keep her safe. Snyder said the apocalyptic world seen in his Justice League would involve "Superman just searching for Batman to kill him to get his revenge for the death of Lois.”
Now that we know Lois' death occurs in the Batcave during these visions, this just adds to the post-apocalyptic future that Snyder was setting up. Superman would probably have taken Lois to the Batcave, thinking she would be safe there under Batman's protection. After Darkseid murders her right there in the Batcave, this would just add to the rage Superman has for Batman after failing to save her.
Fans may never see this future play out, but Snyder definitely had it all worked out in his version of Justice League.