The Full Justice League Story Was All About the Knightmare Timeline
Snyder also dropped some major reveals about the original darker, scary Justice League script. The Knightmare scene in Batman v Superman: Dawn of Justice was far more of a setup than people realized. He said the movies were working up to reach that post-apocalyptic future, all centering around Flash's surprise time-travel visit it Bruce in the Batcave from Batman v Superman.
The way Snyder and Terrio designed the time-travel in the story was that Flash would have to run on the cosmic treadmill built in the Batcave and he would be transported back in time to the same spot in space. That meant they had to choose a moment in time where the Earth was in the exact same location so he didn't end up in the wrong location, or even just land in the void of space.
This left two windows for when he could go back. Batman and Cyborg, who had been damaged and apparently only half of him was left, devised a plan to warn Bruce in the past. This results in what we see in Batman v Superman: Dawn of Justice where Flash arrives in the Batcave and warns Bruce, Lois is "the key" but realizes he's "too soon" and says to "find us."
At the time, Batman didn't understand what Flash was talking about, but once he catches up in the future where it's now his turn to send Barry Allen back, he asks Cyborg which window he'd send Barry through if the choice was his. Bruce then selects the opposite one, knowing the window they chose last time resulted in Flash winding up arriving "too soon."
This is where Snyder drops a major bombshell. The new window chosen for Flash was intended to have him arrive in the Batcave moments before Darkseid himself boom tubed in and killed Lois. As we've learned in the past, Superman goes evil after losing Lois, which makes him succumb to the Anti-Life equation, so Flash's mission was to stop that from happening.
What Actually Made it Into The Version Snyder Shot?
With multiple story revisions between the original script and Joss Whedon's theatrical cut, it's not clear how much of the story Snyder described was intact in the version he shot, but we do know a few details that give us a rough idea of what was sacrificed from the original script.
Snyder described a scene from the trailer where Bruce tells Diana something's coming, "something darker." This quote belonged to a scene where Bruce was explaining how Barry Allen came to the Batcave to tell him Lois is the key. Diana tells Bruce she was the key to Superman because "every heart has one" before Bruce clarifies he was referring to something darker.
Considering this made it into early trailers, but not the theatrical cut, that means it's an element Synder maintained from his original story. We've also seen storyboards of Darkseid in the Knightmare sequence and Synder has clarified in the past that he shoots everything he draws, so while the Knightmare sequence was entirely missing in the theatrical cut, Snyder's original revised script didn't remove that, either.
In the end, fans will certainly never get a live-action version of Snyder's original script, although he could also release the script or turn it into a graphic novel. When it comes to the version of the movie he did shoot, nobody at the Q&A panel asked about that, but we already know significant work was completed on his cut and the distribution rights ultimately remain with Warner Bros. so any decision about getting it released depends on them giving it the green light.