What's in the box? That's what many fans wanted to know when Damien Darhk's mystery box first appeared on screen. Well, last episode, not only did the mystery box appear, it was opened. And given the brief glimpse of the schematics that were unveiled many comic fans think Darhk may have gotten his hands on a Motherbox or Fatherbox - sentient, source-wielding, teleportation devices that belong to the residents of New Genesis and Apokolips (If you're a Destiny player, think of it as a Ghost). There's further chatter that the character's name may be a bit of misdirection from the show's executive producers and that Damien's last name is actually an allusion to his service to Darkseid.
This is an interesting theory but one that merits consideration. Who would've thought that from the gritty realistic season one of Arrow, we'd have a world populated by meta-humans, mystics and very soon, time travel? Given the sheer amount of ground that the show's covered thus far, it doesn't seem entirely out of the question that aliens could be the next topic tackled next season. Coast City, home of Green Lantern has already been introduced. Then, there's the introduction of Hawkman and Hawkgirl. Though the show appears to be going the ancient Egyptian route, it's still not entirely out of the realm of possibility that Legends of Tomorrow somehow weaves in the character's Thanagarian backgrounds. Justice League Unlimited was able to accomplish this with brilliant precision. Lastly, let's not forget that Diggle was just given the codename Spartan; it's entirely possible that the show has already subtly woven in other-worldly elements while directing attention elsewhere.