Cadmus is a name that should instantly make fans of DC Comics and Justice League Unlimited very excited. Primarily depicted as a government organization concerned with creating deterrents to the Justice League and Superman in particular, their typical strategy is to create a clone of Superman that answers only to its creators. The JL: Unlimited cartoon subverted the usual story by having Cadmus create a clone of Supergirl named Galatea. This would actually be more in keeping with the structure of the CBS show, although Kara has already dealt with a clone-esque villain in Bizarro-Girl.
When asked what the Cadmus reveal means for the show moving forward, executive producer Andrew Kreisberg clammed up, stating that Cadmus was being saved for season 2. "We can’t speak to that. You’re not going to see Cadmus this season. It’ll be something that gets saved for season 2." He went on to seemingly imply that they simply don't have enough episodes left in season 1 to do an introduction of Cadmus justice. "We did run out of runway a little bit, so it’s going to remain more of a evil specter-y thing that’s out there. It’s definitely something that we’re going to pursue. Cadmus has such a rich history in the comics and the animated shows. There’s so much there to mine. It’ll definitely be part of season 2."
It will be interesting to see how Cadmus relates to the DEO. Given the close nature and goals of the two government organizations, it seems odd that Cadmus was not mentioned before the last episode.