Contrary to what a lot of fans have theorized for five years now, it seems that the empty cryo-sleep pod in the Scout Ship from Man of Steel wasn't for Kara Zor-El -- or at least, it wasn't that simple.
"The open pod was something more," Snyder said cryptically, then left fans to their wild speculations.
Kara Zor-El -- first seen in the Man of Steel universe as part of a tie-in comic book sold digitally at Wal-Mart -- never got powers in that story, and would be thousands of years old.
Kara, in the David Goyer/Jerry Ordway version of the Man of Steel world, crash-landed on Earth thousands of years ago amid a pitched battle with Dev-Em, her ship later being unearthed and serving as Superman's Fortress of Solitude in the movie.
The Kara introduced in the digital comic was a member of the Kryptonian Explorers Guild, and organization tasked with seeking out suitable planets for terraforming and later colonization by Kryptonians...which basically means she wanted to do exactly what Zod wanted to do, except that back when she first arrived there wasn't a thriving human civilization.
Assuming a follow-up would retain the canon from the comic -- which seems unlikely for a variety of reasons at this point, including that it's not clear how many people actually ever saw the book and, after all, it wasn't onscreen -- the question of how to deal with Kara would be baked into the story. Is she truly an ancestor of Superman's, who came here thousands of years ago? If so, did she remain alive by returning to the ship's cryo-stasis devices, or was she rendered functionally immortal by her powers on Earth? If the latter, does that mean Superman is destined for the same fate?
While it would be easy enough to dismiss the comic as likely non-canonical, bear in mind that the space suits worn by Kara, Dev-Em, and others made a brief cameo in a deleted scene from Justice League, suggesting that someone working on that film still understood the comic to "count."
Considering that Brainiac, who was often rumored to play a role in either a prospective Man of Steel or Justice League sequel, appears instead on SYFY's Krypton, with the involvement of Man of Steel writer David S. Goyer, it could be that earlier plans involved some version of Brainiac's tale interweaving with a pre-Man of Steel Kara.
If we wait long enough, though, it's not unlikely that Snyder, who engages with his fans quite a bit on the Vero social network, will give a little more information on the matter.
h/t Funnel Ferry (Twitter)