After years of campaigning, the Snyder Cut was finally willed into existence in the form of Zack Snyder's Justice League. HBO Max proved to be a blessing for the director's cut to appear on, making it easier to get the movie through production. Excluding credits, the movie runs at nearly four hours long and garnered an overall positive critical reception for fleshing out the film's story arcs.
Fans want a continuation of his universe, as the movie suggests at least a few possible movies that could stem from it. As of now, WB has no intention of moving forward with Snyder's world, though if that stands, video games and comics are other avenues for his universe to continue on.
Video Games: WB Interactive Entertainment
WB has an entire branch dedicated to video game publication with different developers. If more movies aren't in the cards, they could have Snyder's input on continuing the rest of his world based on where Justice League ended. In addition to Justice League 2 and 3, characters like Batman and Deathstroke could easily get games involving them together and individually. Given the emphasis on Cyborg's emotional end of the story, he's another character who could get a game with him as the protagonist.
In the same interview where WB's Ann Sarnoff said they didn't intend to make more Snyderverse movies, she said that gaming is another medium they will dive into with DC properties. Gaming, as opposed to movies, would be a compromise, but it's still a great visual storytelling platform.
Comics: DC Black Label
DC Black Label in particular is a fantastic imprint to publish Snyder's stories under. DC's mainline comics obviously wouldn't fit this, as they have their own long-running, comics-centric stories and series established, but Black Label would fit this like a glove given the liberties and appeal of it.
All books printed by the imprint are intended to cater to older demographics, which is definitely something Snyder likes to gear his interpretations of these characters toward. Plus, all those books are set in alternate canonical timelines to begin with, so there'd be no need to adhere to specific lore established in the mainline canon comics. Snyder's movies are essentially "Elseworlds" stories as is.
Video Games: JL2 & 3 In One Game
In terms of storytelling, video games can easily run longer than any one movie. Gaming has been much more appreciated as a narrative medium over the years, so a single Zack Snyder's Justice League game may be enough to tell the remaining stories from his scrapped JL2 and 3.
If the storytelling is given the care and attention that games like The Witcher 3: Wild Hunt received across ~40 hours, it could easily be done with a Justice League video game. Even non-RPGs like Red Dead Redemption 2 have told extensive stories to critical acclaim with game times an RPG would normally see.
Comics: More Concise "Injustice" Series
The Knightmare world that Justice League and BvS briefly looks into is similar to the premise of the Injustice series, which stemmed originally from the fighting games Injustice: Gods Among Us and Injustice 2. Combining the opportunities offered by DC Black Label and a more concise story, this could be a great place to explore what would've resulted from Darkseid's invasion on Earth for the Anti-Life Equation.
The Injustice comics brought in a hefty amount of books, and since they covered the dystopian DC concept akin to Knightmare already, Zack Snyder's Justice League as a limited series or maxiseries with two main entries could be enough to finish the overall arc without risk of overstaying its welcome in page count.
Video Games: The Next "Batman" Batman Game
WB Montréal--the developers behind Batman: Arkham Origins--are already at work for their next Bat-game in Gotham Knights, though it wasn't what some fans were expecting. It seems to be a Batman-less Batman game, as Bruce Wayne is apparently dead by the start of the game. While focusing on supporting Bat-family members is a fun twist, the next game focused on the titular superhero is still a mystery.
As planned before and further delved into with ZSJL, it's suggested that Ben Affleck's The Batman was set to involve a Knightfall and Arkham Asylum-inspired narrative, but with Deathstroke instead of Bane. While the longest of longshots, perhaps getting Affleck to lend his voice and likeness to a game would be a great way to bring that story to the screen.
Comics: More Black-Label Batman
Staying on Affleck's original movie and Black Label, the imprint could suit this even better, as it's already proven quite kind to Batman to this day for alternate-timeline stories. Sean Murphy is writing an ongoing maxiseries with White Knight and others writing spinoffs, and Scott Snyder has written Last Knight on Earth and Geoff Johns' recent Three Jokers.
The premise of what Affleck's Batman movie would've been would be perfect as a one-off limited series the length of White Knight or Curse of the White Knight individually. ~250 pages should be plenty to give his story good amounts of substantive, impactful storytelling. This would also be easier to put together than a game.
Video Games: Marketing Power Of A Triple-A JL Game
Though Square Enix's Avengers game ended up squandering the potential of the power behind the brand and characters with live-service models and overly-repetitive gameplay, WB could amass goodwill by giving this the budget and creative liberty of a triple-A game that would support characters as beloved as Batman, Superman, or Wonder Woman.
While comics are a fantastic source of iconic stories, a triple-A game will garner more traction and popularity than another comic book series, since the Justice League has plenty going on as is in DC's comics world. If live-action movies and/or TV shows aren't coming, gaming is the next best way to put Snyder's completed world on-screen.
Comics: JL2/3 Series With Spinoffs
This isn't anything new to DC's line of comics, with Batman--for example--having Batman along with Detective Comics, Urban Legends, Nightwing, The Joker, and more. Detective was the flagship for the character's inception and isn't exactly a spinoff, but the latter two are a perfect example of spinoffs of the main series.
A hypothetical Justice League 2/3 series could similarly lead to spinoffs like the mainline Batman and other superhero comics often do. Running in between or concurrently with Justice League 2/3, at some point an Affleck Batman comic, Jason Momoa Aquaman comic, or Henry Cavill Superman comic could splinter off to grow the world out.
Video Games: Story-Focused, Optional Co-Op
To avoid the issues with SE's Avengers, WB Games could make Snyder's continued story work by taking a page from what appears Gotham Knights is doing. The latter game isn't out--it even got delayed to next year--but on paper, what it's planning to do with its gameplay format could work for a Justice League game.
Ditch the live-service model altogether and focus on a good, substantive plot with engaging gameplay, but include optional co-op mechanics. Gotham Knights is said to playable by a single player without missing anything, but a friend can pop in to control another character too. It'd certainly necessitate character balancing, but if executed well this could be a thrilling style with genuine replay value.
Comics: Chris Terrio Writing
A way for Snyder to continue his story arc continue and finish in comics could be getting someone he's already worked with to write for to comics, for instance, Chris Terrio. It's another stretch given the lack of work in comics, but it could work with how DC is handling their Batman '89 series.
Writer Sam Hamm is returning to write in Burton's world (as he was a writer on his Batman and Batman Returns movies) so the series can keep the spirit of the original works. Persuading Terrio to at least oversee the writing of Snyderverse comics could be a good way to flesh out the story as intended.