Why Was Snyder Moving Forward So Fast?
Needless to say, this all seems contrary to the narrative put forward and makes even less sense considering the big changes that were ultimately implemented. It's long been rumored that a December screening of an early cut of the movie was considered "unwatchable" by at least one person. If this was the case, then why would Snyder move to picture lock so soon if it was clear that rewrites and reshoots were going to happen? The simplest and most logical answer is that the original plan was for this version of the movie to be seen.
The reason there's such a strong push behind the notion of a Snyder Cut in the first place is because Snyder already has a track record of releasing longer director's cuts. Dawn of the Dead, Sucker Punch, Watchmen, and Batman v Superman have all had longer cuts released, and in each instance, the longer cut is seen as the superior version. If Snyder was moving full speed ahead with this cut of the movie, it only makes sense that he expected Justice League to follow suit.
Zack Snyder movies have always been polarizing, so it's hard to contextualize exactly what it means for his early cut to be dubbed "unwatchable," but with a studio-mandated runtime of under 2 hours for the final product, it could have just been "unwatchably long," especially if he didn't significantly lighten the mood from Batman v Superman. The final Warner Bros. approved product was visually brighter (frequently to the point of oversaturation), tonally lighter (including some controversial groan-worthy Whedon one-liners), and under 2 hours. Considering each of those points are clear alterations from the original version, it speaks to what exactly WB execs thought was missing from Snyder's cut, which means it very well could have delivered exactly what his ardent fans expect from him, and what his detractors dislike.
This strongly suggests that the initial reports that Joss Whedon was merely punching up some dialogue and creating some connective tissue may have been true, meaning the release of a longer, darker Snyder Cut wasn't out of the question, as Snyder was clearly full speed ahead with his cut. If that's the case, then the decision to alter the movie as drastically as it was may have only been a decision that was made after Joss Whedon took full responsibility for the reshoots and the studio saw an opening to take the movie in a drastically different direction.
So, based on this evidence, we can know with a fair amount of certainty that the Snyder Cut is picture locked and color graded with a good amount VFX and audio mixing completed, corroborating the report claiming it exists in 'relevant form', with the only major caveat being that there's no evidence to suggest Junkie XL's score was completed before he was fired (although it's not out of the question). This will doubtless please a number of fans campaigning for the release of the cut, but, unfortunately, it doesn't mean it's guaranteed to ever be released.
Unless Snyder plans to leak it himself in defiance of the studio (what some may call career suicide), it's ultimately up to Warner Bros. to provide the funding to polish it up and distribute for home release, which the studio has limited incentive to do. If the Snyder Cut is inferior to the Whedon cut, then there's little reason to release it, but if it's superior, then the studio will have even more egg on their face than they already have after Justice League's numerous failures from bad critical reviews and a botched box office to memes over Henry Cavill's bad mustache erasing CGI - which has quickly become the poster child for Warner Bros. handling of the entire issue.