[Warning: SPOILERS for the Supergirl season 1 finale ahead.]
The Marvel Cinematic Universe may still be the king of superhero cinema (at least far as critics and box-office returns are concerned at the moment), but the DC Extended Universe is seen by many as far and away the champ where broadcast television is concerned. Arrow continues to hold a dedicated fanbase, The Flash draws bountiful praise with its happy-go-lucky take on superheroics and even Fox's divisive Gotham boasts devout weekly viewers. 2015 saw the addition to this menagerie of Supergirl, a lighthearted but high-stakes adventure that won critical praise and excited fans with the DCEU's first "multiversal crossover" between networks.
Despite this, however, Supergirl has also been slower than the other DC TV shows currently on the air to earn a season 2 order. However, with the show's first season having wrapped up on a major cliffhanger ending (with several major plot-threads left hanging), co-creator/executive producer Ali Adler seems confident that big things are yet to come for Kara Zor-El and friends.
The Supergirl season 1 finale saw Kara (Melissa Benoist) rescue National City from impending doom, re-solidify her budding romance with James (formerly "Jimmy") Olsen and in general become poised to head into future adventures with her confidence cemented and her life (mostly) in order... until a Kryptonian space pod eerily similar to her own crash landed near her home. Audience's didn't get to see exactly who (or what) was inside the pod, but Kara did - and whatever it was shocked her. Asked if the show's producers have already decided who/what the pod contains by TVLine, Adler explained:
"Hashtag-who-or-what-is-in-the-pod. We’ve absolutely had conversations — we’re waiting to tell CBS. In the spirit of good, old-fashioned cliffhangers, we certainly answer many more questions in terms of her trajectory with Jimmy Olsen, her relationship with Alex. We prove what an incredible hero she is. She was sent to save this world, and she does."
The Supergirl season 1 finale actually left several plot threads and long-running story arcs unresolved, including the introduction of a DCEU version of The Omegahedron (the MacGuffin from the infamous 1980s Supergirl movie with Helen Slater, who plays Kara and Alex's mother on the new series) and the lingering issue of Kara's supposedly dead adopted father Jeremiah (onetime Lois & Clark Superman Dean Cain) actually being alive and a prisoner of Cadmus. The mystery of the pod unsurprisingly became the focus of many fans as soon as the episode concluded, with the series' powerful social-media following exploding with theories about who (or what) might revealed should the series receive a season 2 renewal.
One theory that gained immediate traction was the pod's occupant could be a DC Extended Universe version of "Power Girl", aka the Supergirl of Earth 2. Much like the DCEU now, the DC Comics universe was prior to 1985 comprised of multiple parallel universes (or "Infinite Earths") that often featured "alternative" duplicates of known characters; with Power Girl originating as a slightly older, more jaded incarnation of Kara Zor-El who eschewed connections to her cousin Superman in the name of militant-feminist independence. Though her Earth was deleted from continuity, Power Girl lived on in the new post-Crisis DC continuity largely thanks to fan popularity and (many have posited) because DC artists were fond of her revealing costume choices.
Other potential pod-person theories that seemed immediately popular included a DCEU version of Superboy (originally a teenage Clark Kent getting an early career start, but the title has been claimed by others since) and Krypto the Superdog - who, in classical DC Comics lore, is Kal-El's (Superman's) puppy from Krypton, sent into space ahead of him as a safety test but arriving on Earth later and imbued with the same super-powers as his master (though Supergirl is traditionally more associated with Streaky the Super Cat and Comet the Super Horse, as far as pets go). Other more out-there guesses included Miss Martian (a female equivalent to Martian Manhunter, himself already established as part of Supergirl's supporting cast) and the Cyborg Superman, a villain introduced as part of the infamous Death & Return of Superman storyline.
Obviously, answers will have to wait until when and if a second season is confirmed, though according to Adler fans should feel optimistic:
"We heard very positive things, unofficially, from Les Moonves. [CBS Entertainment President] Glenn Geller and [executive vice president of current programs] Bridget Wiley — they’ve all been very, very supportive. We’re definitely talking about what Season 2 looks like."
We'll let you know if (when?) Supergirl gets renewed for season 2.