In episode 10 of Legends of Tomorrow, it was revealed that Ray Palmer has a brother named Sydney, who went on to become the Atom after Ray disappeared from the timeline. It was also revealed that Sydney went to work for Felicity Smoak during her tenure as CEO of Palmer Technologies before eventually founding his own company, Kasnia Conglomerate. With that knowledge of the future, it seems inevitable that Sydney will show up on Arrow at some point, right?
"[He] is a potential Arrow character", said executive producer Marc Guggenheim. However, he went on to add, "[But] we’ve actually been talking about seeing [Sydney] in Legends Season 2." Guggenheim also clarified that Sydney and Ray are not twins, they just look nearly identical (as evidenced by the bust at Kasnia Conglomerate).
Not much is known about Sandy Palmer. He could be one of the good guys or a villain. And given the fact that we never actually met him in Legends of Tomorrow, it's possible that Sydney could end up being one of the team's new additions in season 2. Just apply some make-up to Routh and he could play a brand new character.