“Elseworlds” was a DC Comics imprint that took familiar characters and changed something about them or their world. The books were set in their own continuity so creative freedom reigned. It’s akin to Marvel’s “What If,” though the ideas of “Elseworlds” tended to be grander, rather than the changes to particular stories you would find in “What If…?” issues.
Take “Batman: Gotham by Gaslight” by Brian Augustyn and Mike Mignola, which reimagined Batman in the 19th century, or “Superman: Red Son” by Mark Millar, which depicted a world where Superman was raised in the Soviet Union instead of the USA. Todd Phillips’ 2019 “Joker” (aka “What If… ‘The King of Comedy’ was bad?”) was described as an “Elseworlds” film, since it was so far removed from the traditional DC Universe. James Gunn’s interest in Elseworlds stories bodes well not just for Todd Phillips, but also for Matt Reeves and Robert Pattinson, who may not have to have their Batman folded into a shared universe after all.
Frankly, DC Comics has never been as good at maintaining a shared universe as Marvel. The Marvel Universe was the product of Jack Kirby, Steve Ditko, and Stan Lee, with subsequent writers and artists building off of a singular foundation. With DC, the staple characters were all created by different people and welded together. That means the characters lend themselves better to variety and stories that don’t rely on continuity. Based on his own superhero films, Gunn cares about character first and if one of DC’s roster fits an Elseworlds story, it sounds like he’ll be open to pursuing it.
According to Gunn himself, he and Safran will be sharing their plans early into 2023. It sounds like we can expect some Elseworlds projects on the slate.