With a Kryptonian big bad and at least a few Kryptonian villains kicking around -- plus Superman off in Metropolis -- it seems pretty clear that CBS's Supergirl is not particularly shy about going back to the homeworld for story ideas.
There's a rich history there -- and there are, of course, a handful of different takes on Krypton that can be mined. There's the kind of "cult of science" that was established during the Byrne era; there's the Silver and Bronze Age sun god-worshipers, there's the World of New Krypton material in which Superman and Supergirl struggled to find a role for themselves when there are tons of Kryptonians on Earth, and much more.
So...which of these could be really entertaining TV? We've got some ideas...
When we recently asked Superman: Lois and Clark writer Dan Jurgens what he would like to bring back from the pre-Flashpoint DC Universe (where he wrote Superman for nearly a decade), Jurgens was unequivocal: The Eradicator, a small, Kryptonian artifact which had set in motion so many stories throughoug the '90s and the early part of the new century.
A weapon designed to "purify" Krypton following a clone war, The Eradicator was invented by a member of the House of El, meaning that its introduction -- especially if it means trouble, which it almost always does -- can be frustrating for Supergirl, who could feel guilty about its creation, frustrated with her parents for not sharing details with her etc.
And, of course, it has been known to periodically take over the minds of Kryptonians and essentially make them "more Kryptonian," which could be an interesting snag to hit when the big bad of the season is Kryptonian herself.
We've already seen that some of the Kryptonian military garb resembles what we see above.
Could we see more elements of Kryptonian culture, as depicted in the World of New Krypton storyline, reflected in Supergirl? Given how much they love the Sterling Gates/Jamal Igle issues of the Supergirl comic, it seems almost inevitable, really.
But we'd love to see beyond just the military guild and get a feel for some other elements of Kryptonian culture...something that's often glanced over to make way for the punching.
THE BOTTLE CITY
The Bottle City of Kandor is probably the most storied part of Krypton's lore...and arguably the hardest to deal with at the moment.
Why? Well, Kandor is tied with Supergirl in a big way: it's the capital city of the planet, which was saved from Krypton's destruction only to be captured and shrunk down by Brainiac. In World of New Krypton, Supergirl has family there, which complicates her dynamic with Superman the humans...
...but of course, it's hard to imagine that Brainiac is fair game. One of Superman's most popular and enduring villains, he's constantly being rumored as a potential bad guy for an upcoming Superman or Justice League film.
That said -- if you're going to bring in a bunch more Kryptonians, which doesn't seem unlikely at this point, you really have to do it with Kandor. Anything else would feel like cheating, since Kandor is such a big part of the mythology. And by having it, we can introduce some version of Nightwing and Flamebird, the city's vigilantes.
One interesting element of Krypton is its religions.
In JLA recently, Bryan Hitch wrote a story in which Rao, the Kryptonian sun god, was a villain. That deity was the default for years when talking about Krypton, but during the post-Crisis on Infinite Earths/pre-Flashpoint era there was a chunk of time where there simply wasn't really a modern religion on Krypton, a world that had become increasingly cold and scentific. You can see many of Byrne's high concepts reflected in the Man of Steel movie.
Both of those belief systems could create some interesting conversations, and especially if you were going to introduce the Eradicator, the character of the Cleric (seen above), an ancient religious figure who was forced offworld as a means of suppressing the practice of religion. Cleric was an interesting character and a useful figure in terms of expository dialogue during the "Exile in Space" storyline.
To fans of the movie, the Black Zero is Zod's spaceship...but we've already seen that the Krypton of Supergirl isn't exactly the same as the Krypton of Man of Steel.
After all, the S shield has different meanings in each.
There have been a number of different takes on Black Zero over the years, although the one that they generally seem to go back to is a terrorist group responsible in whole or in part for the destruction of Krypton.
There's also the version seen above, essentially an adult version of Superboy who is evil and likes to mess with reality. That one, in particular, could be adjusted to fit Supergirl pretty easily and give her a formidable foe -- although it might be better to wait on that to find out if the show gets its expected second season, since "evil doppelganger" is not only done a ton in comic book movies but it's being done for the second year in a row on The Flash right now.
Black Zero is a name shared by two supervillains, two terrorist organizations, one special forces group, and a computer virus that have all appeared in various comic book series published by DC Comics, though, according to the concept's Wikipedia entry, so it's not like they couldn't use the name somehow.