Director Gareth Evans is shedding some light on what his Justice League's post-credits scene, which introduced Manganiello's Deathstroke and put him in with Lex Luthor (Jesse Eisenberg). The two seemed to be gearing up to create the Legion of Doom, but following the disappointing reception to Justice League, things seemed to change.
While Manganiello was still optimistic that Deathstroke would come to back in 2018, it was only a few months later that Green Lantern Corps.
While speaking to Yahoo Movies UK, Evans said he was "quite enthused and excited" when he was initially attached to Deathstroke, and he conducted a fair amount of research during that time. Evans' plan was to tell "a lean story, that would be kind of an origin of that character. Something that felt like it could be 100 minutes or 110 minutes long, max – not to go over the two hour period with it." Considering how some moviegoers complain about unnecessarily long films, this likely would've been a well-received plan.
Evans went on to say he was influenced by South Korean noir films, and he would've tried to implement that style into Deathstroke. As he explained, "I was like, these films are amazing: the texture, and the tones of colours, the grit and the aggression of them is super interesting to use to tell Deathstroke's story." This matches up with Evans' previous comments regarding the film. The origin story aspect would likely place Evans' Deathstroke ahead of Justice League in the DCEU timeline, since the character's appearance in the post-credits scene already had him as an established mercenary.
The DCEU will continue with new solo films centered on Wonder Woman (Gal Gadot) and Aquaman (Jason Momoa), but it's unclear how connected their future installments will be. While Eisenberg previously said he would be open to returning as Lex, it seems unlikely at the present moment that he will, suggesting any plans for a Legion of Doom film are dead. Of course, that could always change should Warner Bros. and DC decided to revisit it, but Evans' comments on the matter make it seem like Deathstroke won't ever come to fruition.
Source: Yahoo Movies UK
