Zack Snyder's Justice League 2 was supposed to release today, but instead, fans are still campaigning for his version of the original Justice League, which we never got in theaters. It's well known by now that the progenitor of the DCEU had a five-part story to tell for Superman and the Justice League, starting with Man of Steel and culminating in a Justice League trilogy with the Man of Tomorrow at the center of it all.
Instead, after a family tragedy, Snyder was pushed off of Justice League, despite being deep into post-production, and Joss Whedon was brought on to rewrite, reshoot, and otherwise overhaul Snyder's movie into something Warner Bros. thought would be a more palatable and mainstream movie.
Not only did the effort not garner the movie any favor with critics and bomb at the box office, but it quickly became a meme for it's shockingly obvious reshoots and Henry Cavill's CGI upper lip. Needless to say, if Zack Snyder's Justice League 2 wasn't already off the table, Justice League's theatrical cut was the final nail in the coffin.
Nevertheless, with such a bold and polarizing vision for the universe attracted its share of passionate - or just plain curious - fans. The quest for the Snyder Cut (which Snyder says is real)has unearthed massive changes to the movie's tone and story, creating even more interest in what Snyder would have brought to the table with Justice League 2. We may not have the full picture yet, but a number of things about the plot for Justice League 2 have come to light in the last 18 months.
How Zack Snyder's Cut of Justice League Was Supposed to End
Zack Snyder's cut of Justice League was supposed to be over 3 hours long and would have introduced mega villain Darkseid, including a cliffhanger moment at the end where he reveals himself to the League after they defeat Steppenwolf.
While much of the movie was significantly altered or removed, the larger brushstrokes of the ending for some characters is consistent with what Snyder intended, but there are also some significant differences for others. Superman is back in Metropolis (and brighter than ever), Bruce Wayne has started to convert Wayne Manor into the Hall of Justice, Flash had learned to time travel (for just a few seconds) in the 3rd act to save the day, and Cyborg has embraced himself as a hero and the closing monologue would have been from Silas Stone, not Lois Lane, giving an inspiring message to his son via a recorded message. While Silas lived in the theatrical cut, he was supposed to die in the Snyder Cut. Cyborg was supposed to be the heart of the movie and would have also been shown to have the power to rival even Superman.
Snyder shot 100% of Justice League's script (including scenes with actor Ray Porter, who had been cast as Darkseid) and was deep into post-production when he left the movie. If that plan hadn't been scrapped and hastily redone at the final months of production, the Darkseid cliffhanger at the end of the Snyder Cut would have set up Justice League 2, which would have been produced and released by now barring any production delays.
Justice League 2 Never Had a Script Written
While Zack Snyder's whole five movie arc was planned out, Justice League 2 never had a proper script, and didn't even have a writer assigned yet. Chris Terrio rewrote David Goyer's Batman v Superman: Dawn of Justice script and wrote Justice League, but said before Justice League started shooting that he wasn't sure if he'd write Justice League 2 or not.
Since Justice League was rewritten in response to Batman v Superman: Dawn of Justice's critical hammering, Justice League 2 would have also presumably needed some adjustments to match. However, the overall story doesn't seem to have been scrapped so much as toned down, meaning the main plot points we know about Justice League 2 would presumably stay mostly the same.
The Villain Was Darkseid
Darkseid was to be introduced in the first Justice League, with Steppenwolf being the primary antagonist (think Sauron and the Nazgul in The Fellowship of the Ring), but Justice League 2 would have seen the League face off against Darkseid directly.
Justice League's history lesson would have set up Darkseid using the Anti-Life Equation (a formula that eliminates free will), although Darkseid was replaced with Steppenwolf in that scene for the theatrical cut, so while the fiery symbols that etch into the ground when Steppenwolf hits it with his hammer were intended to be the Anti-Life Equation, this was never specified in the theatrical cut.
The most logical story would have been something at least loosely inspired by Grant Morrison's Final Crisis, a story that sees Darkseid invade Earth and subdue humanity with the Anti-Life Equation. Snyder shares a number of story sensibilities with Grant Morrison, and in addition to the relevance of the Anti-Life Equation, there's some additional plot points that support Final Crisis as inspiration.
The Knightmare Was Important
The Knightmare timeline first established in Batman v Superman: Dawn of Justice is entirely absent in the theatrical cut of Justice League, but it was originally meant to be a much bigger deal for the original five-part arc, and is likely what tied the whole story together.
The original Justice League script saw Darkseid boom tube into the bat cave to kill Lois Lane, whose loss makes Superman susceptible to the Anti-Life Equation, putting him under Darkseid's control and setting off the series of events we see in Batman v Superman: Dawn of Justice's Knightmare, eventually resulting in The Flash jumping back in time to warn Bruce, only from the events of Batman v Superman: Dawn of Justice we know that he was "too soon" so Bruce isn't able to understand what Flash is talking about yet and may have misinterpreted the warning to be about Superman instead of Darkseid.
In the Knightmare timeline, Batman and Cyborg build Flash a cosmic treadmill in the Batcave. Using the Treadmill, The Flash can jump through time, but since he's staying stationary in space as he does it, he can only jump to specific points in time where the Earth is in the exact same location in space or he'll just time jump into a vacuum.
After Knightmare Superman kills Batman, Cyborg identifies 2 windows Flash can jump through to lead him to a time before Darkseid killed Lois where the Earth is in exactly the same position. Cyborg chooses one of the windows, but when Flash arrives, he realizes he is "too soon." However, now that Batman has been warned about something, Luthor's seemingly unhinged rant at the end of Batman v Superman: Dawn of Justice tips him off that he needs to prepare for "something darker," possibly leading him to form the Justice League earlier than in the Knightmare timeline.
The exact sequence of events isn't clear, and the script would have been changed to align with the Justice League rewrite, but it's possible Bruce still isn't able to stop Darkseid from killing Lois, resulting in the Knightmare timeline again, only this time he knows that whatever window Flash chose was "too soon." This time, Bruce asks Cyborg which one he would choose, and after Cyborg identifies a window, Bruce chooses the opposite one, choosing a point in the timeline that allows them to save Lois and prevent the Knightmare timeline from ever happening.
Green Lantern Would Have (Maybe) Finally Arrived
Justice League 2 would have (probably) finally been the introduction of Green Lantern. Of all the things we know about Snyder's plan, exactly how Green Lantern fit into it is one of the most unknown aspects, but he did tease Justice League 2 as the movie where it would happen.
At one point, there was a post-credit scene planned for Justice League where Bruce wakes up in his lake house to a green glow and encounters the Green Lanterns Killowag and Tomar-Re, but it appears that concept was abandoned even before Zack Snyder left Justice League.
Charles Roven is said to have been a big fan of Mark Wahlberg and wanted him as Green Lantern (explaining an image of Wahlberg posing with portraits of the BvS cast in his office), but nothing was ever finalized.
Batman Would Die in Justice League 2
Snyder has also confirmed Batman was going to die in Justice League 2. The exact nature of his death isn't known, but he sacrifices himself to kill Darkseid in Final Crisis, Batman was expected to sacrifice himself to defeat Darkseid. This has caused a bit of fan outrage, but makes a lot of sense if you understand the context of what Snyder was doing with his DC movies.
Ben Affleck didn't ever sign up to be the next Robert Downey Jr. or Hugh Jackman. Affleck had already sworn off the superhero thing after a disastrous Daredevil outing, but Snyder's older, grizzled take on the character won him over. The fact that it would be just a handful of movies and he'd be done was surely also an appeal.
How Zack Snyder's DCEU Ended
As a part of a charity T-Shirt campaign, Snyder released a shirt full of a variety of classic and mystical symbolism identifying the full arc of his five-part movie franchise.
There's a lot of vague and layered meaning to the symbols, so we don't have to break the whole thing down fresh here, but one major reveal from the shirt is confirmation that Batman sacrificed himself to save Lois and Lois and Clark go on to have a child who they name Bruce (as confirmed by Snyder on Vero). This is obviously a huge full circle moment after the conflict of Batman v Superman: Dawn of Justice.
Having Superman reproduce and name his child after Bruce shows not only a resolution to the opening of Man of Steel, where Kal is the first naturally born Kryptonian baby in generations, but now he's also had a natural child of his own, spreading the hope of Krypton to Earth as Jor El intended.
While the Snyder Cut of Justice League is significantly complete and could be released, Justice League 2 unfortunately only lives as a basic story treatment and maybe some early concept art at most. While this story is doubtful to ever be fully realized on the big screen, there's an argument to be made in favor of it being adapted to a graphic novel or animated film so fans can see the rest of the story Snyder had planned and bring a semblance of closure to the whole situation.