The Arrowverse, but the DCEU could be taking this to a new level.
Batman universe, it raises the possibilities of a number of additional worlds being brought into this expanding Multiverse. There's a variety of both comic book and cinematic universes worth exploring as part of the DCEU.
Honorable Mention: Mortal Kombat And Injustice
The successful comic book series and the NetherRealm video games have resulted in the long-lasting Mortal Kombat. With Warner Bros. owning all of these properties and the recent release of the Mortal Kombat film, a crossover like this could be in the cards.
The selling point of Injustice as a narrative surrounds the corruption of Superman. After the death of Lois Lane at the hands of the Joker, the Man of Steel creates a new global regime that he sees as a form of protection for humanity. It's a grim story that could mesh well into the current DCEU.
Earth-Two
Aside from the fact that it opens the door to a variety of potential new Justice League , the existence of Earth-Two could usher in a new era of storytelling for the Worlds of DC line. The concept of Earth-Two in the comics is that it houses many of the classic, Golden Age characters.
The original portrayals of some of DC's most iconic heroes like Jay Garrick or Alan Scott all inhabit this alternate Earth. To see some of these stories brought to the big screen would definitely be exciting and it would allow for the DCEU to take on a slightly different tone.
Amalgam
The Amalgam universe will likely never receive an adaptation to the screen (big or small) thanks to the complexity of the legal issues surrounding the creation. Amalgam saw both DC and Marvel work together on heroes that combined some of their own characters' costumes and powers.
With odd alliances and a brand new set of heroes and villains to explore, comic book fans were engrossed in this unique creative endeavor. Ultimately though, despite how incredible it would be to see this, it's impossible to imagine DC and Marvel Studios working on a project together currently.
Gotham By Gaslight
A number of Gotham-based projects were announced, which have likely been canceled without official confirmation. From heroes like Batgirl to the return of villains like the Joker, many of these DCEU stories have been canned so the universe can go in an alternative direction.
Despite this, when looking at completely different universes, the Gotham By Gaslight iteration of the famous city is definitely worth visiting. It's a 19th-century version of the DC Universe, with each of the company's main characters getting a steampunk-esque makeover. It boasts a great narrative and a unique aesthetic for the big screen.
Dark Knight
The Dark Knight universe, created by Christopher Nolan, redefined superhero films. With the series containing some lasting performances including that of the late Heath Ledger, there have been many fan discussions about one day revisiting this popular version of the Batman world.
With some intriguing worldbuilding and a great take on the mythos, there could be a future for the Dark Knight universe as Man of Steel crossover. He noted that Joseph Gordon-Levitt's Robin would have suited up as the Caped Crusader!
Arrowverse
The Arrowverse boasts some of the most Crisis On Infinite Earths story, the DCEU's Flash even made an appearance alongside the Barry Allen of the CW. This was a highly regarded moment for the company.
It demonstrated that there was a possibility that these crossovers could be pushed further in the future. A full-scale connection between the Arrowverse and the DCEU would definitely be a welcome one for hardcore fans. Perhaps multiple Barry Allens could be present in the future Flash film.
Dark Multiverse
The Dark Multiverse is a recent creation that has completely flipped the DC Universe on its head. With these negative Earths existing in the comic book reality, some of DC's most important heroes have taken a dark twist in these alternative settings.
The most iconic of them all is the Batman Who Laughs, a strange mixture of both the Dark Knight and the Joker. This universe would therefore allow DC to ignore low-level criminals and instead push the Justice League to their limits against the Multiverse's most despicable creatures.
Future State
The Future State universe is another recent addition to the comics, but one that has huge potential. It shows what could happen to the Justice League in one of many plausible futures, thus allowing new heroes to rise. DC has therefore boldly recreated their famous characters.
With a new, diverse set of warriors behind the masks, the DC Universe has been reborn. A Future State universe on the big screen would allow Warner Bros. to explore the future of their famous franchises while still capitalizing on the classic iterations of these characters.
Joker
The Joker has been put to screen on many occasions, with each performer putting their own unique spin on the role. Joker grounded the Clown Prince of Crime in a more realistic setting and explored his origins as a failed stand-up comic living with mental health issues.
It's a dark and psychological tale, but fans are already curious to see how this Joker would respond in a more comic book accurate universe like the DCEU. Pitting Joaquin Phoenix's Joker against Ben Affleck's Batman could lead to a compelling and unexpected dynamic.
Alas, there appear to be no plans to adapt the canceled projects on the Warner Bros. floor. There's one path that could make fantastic use of Alan Moore's characters, though.
The comic books have already seen the Watchmen universe and the traditional DC Multiverse collide and there's no reason the DCEU couldn't achieve something similar. Fans are now well-versed in the Watchmen world and it would be exciting to witness Dr. Manhattan and Superman or Sister Night and Batman collide for the first time.
