From the sounds of everything he's looking to add in (or add back), Zack Snyder really is intent on justifying the four-hour running time for his Justice League limited series/extended movie. The latest news comes via Collider that Joe Manganiello will shoot more scenes as Deathstroke.
Unlike Jared Leto's Joker, who will be a completely new addition, Deathstroke actually appeared in Justice League's theatrical cut, albeit limited to a post-credit scene where he's recruited by Jesse Eisenberg's Lex Luthor to form a group of villains. According to Collider's sources Manganiello will be shooting new material as Deathstroke, as opposed to Snyder digging up unused material. There is, of course, no official confirmation yet, so we're going to have to wait to see whether he's actually returning and what part he plays in the story.
Snyder has already been shooting additional footage with the likes of Ben Affleck, Ray Fisher(Cyborg) and Amber Heard (as Mera), for his expanded and alternate Justice League, due on HBO Max next year in four hour-long episodes.