Zack Snyder's Justice League is in many ways representative of the DC Extended Universe getting its second wind. Causing an immense amount of hype around the time of its announcement, the official release of the so-called "Snyder Cut" will itself be a second chance for the universe and Justice League. Not only will it be far truer to Snyder's original plans for the universe, but it could also give a glimpse of its future by better showcasing the directions of certain characters.
Several key DC villains are having roles expanded or even created for the film through additional scenes, and it'd be a waste for these to just be glorified cameos. In bringing in Joker and Deathstroke, Zack Snyder's Justice League has given itself the chance to have the bad guys officially form a league of their own.
The reports of villain actors coming back to shoot additional scenes concerned Jared Leto reprising his controversial role as The Clown Prince of Crime, although this news doesn't exactly spell out what kind of role the villain will play in the film, or where chronologically his scenes will take place. This was followed up by news that Joe Manganiello would be returning to shoot additional scenes as Deathstroke for the greatly expanded version of the film.
One of the biggest complaints about the theatrical version of Justice League, besides its rushed nature, was that its overall quality and story direction left no real excitement for the future of the DCEU. This was in spite of the post-credits scene, which pretty blatantly set up the formation of the Injustice League. By taking this concept and expanding on it, Zack Snyder's Justice League could make it into much more of a hook for future films. The ending scene in which Slade Wilson meets Lex Luthor will likely be expanded upon, but some of the added Deathstroke scenes will likely take place beforehand. This could be used to generate audience interest in seeing more of the villain in later movies, as opposed to the one-hit-wonder that Manganiello's take on the character had seemed to be.
The new scenes with Joker could catch audiences up on where the Clown Prince of Crime has been, as the events of Suicide Squad and Birds of Prey have left him without Harley Quinn. Likewise, these scenes could redeem Leto's take on the character, which has been widely criticized since 2016. Other scenes could even somehow foreshadow Black Manta or Sivana joining the team, as well as possibly Cheetah if the villainess survives into the modern-day following the events of Wonder Woman 1984.
This would make the ending of the heroes' teaming up the beginning of the journey to see the villains do the same. It would also secure, so to speak, a place for these characters in the future of the DCEU, which is very much turning a corner by otherwise going in a different direction than before. The villains could appear, even if in minor roles, in further movies for their respective heroes. Deathstroke could even get his own movie to further flesh him out, as was planned at one point. If successful, this could also make the possibility of a Justice League 2 featuring the Injustice League more of a possibility.
While this all could definitely be far too much in a film that many already believe will be severely bloated, it would be doing the foundational work that the DCEU never did for Justice League. By hyping up the villains' teaming up across several movies' timespan, the mistake of simply jumping into a crossover to imitate The Avengers won't be repeated.
Justice League stars Ben Affleck as Batman, Gal Gadot as Wonder Woman, Henry Cavill as Superman, Amy Adams as Lois Lane, Jason Momoa as Aquaman, Ezra Miller as The Flash, Ray Fisher as Cyborg, Jeremy Irons as Alfred Pennyworth, Diane Lane as Martha Kent, Ciarán Hinds as Steppenwolf, Jesse Eisenberg as Lex Luthor and J.K. Simmons as Commissioner Gordon. Zack Snyder's Justice League will premiere exclusively on HBO Max in 2021.