The crossover between Supergirl and The Flash was a resounding success, resulting in an episode that was fun, thrilling, and set up many exciting possibilities for the future of all DC TV shows. This is mostly thanks to the DC multiverse, a setting which allows pretty much anything you can imagine to happen.
The multiverse means that many different versions of Earth are possible within one fictional canon, as Barry Allen explained.
Not only does this mean that we could see many more crossovers between Supergirl and the Flarrowverse, it also sets up another exciting possibility...
Does All Of DC Exist In The Same Canon?
DC has many different properties spread across three TV networks and of course the Warner Brothers films. Unlike the Marvel Cinematic Universe, which combines the TV shows and films into one canon, DC is rather fractured. Until now.
The Supergirl/Flash crossover was exciting because it bridged the gap between two networks: CBS and the CW. Such crossovers are rare because of copyright concerns. But thanks to Worlds' Finest, the possibility is now open that another DC show, Gotham (airing on Fox), and even the DCEU films exist in the same canon multiverse as Arrow, The Flash, Legends Of Tomorrow, and Supergirl.
Of course, a crossover between the movies and TV shows is unlikely. But an epic team-up with Arrow, Supergirl, Flash, and Gotham's young Bruce Wayne is not only possible, it's already being considered by the network execs.
Supergirl's executive producer, Andrew Kreisberg, discussed future crossovers with Deadline.
"We would love that. I think it’s really up to the respective networks and what their appetite is for it, and certainly the audience. If there’s a strong audience response to the Supergirl and Flash crossover, that’s certainly the wind in the sails to try and make it happen again."
Worlds' Finest prompted an overwhelmingly positive reaction from fans, so it's safe to say that Kreisberg got the "strong audience response" he was hoping for. So where could all of this lead?
The possibilities for the DCTV multiverse are really exciting, especially considering some of the plots from the DC comics canon.
Building Up To A Crisis
Because of its impressive 50 year plus run, DC has multiple continuities which can be quite confusing. There have been several canon resets to try and organise these into one coherent continuity. When it comes to the multiverse, the most important resets are Crisis On Infinite Earths (1985) and Infinite Crisis (2005).
Both of these plotlines are very complex, but the upshot of it is that Crisis On Infinite Earths combined the multiverse into just one Earth, effectively removing Earth-Two and other Earths from the canon. Infinite Crisis reintroduced survivors from Earth-Two, including Power Girl's origins as the Earth-Two Supergirl, and restored the multiverse.
Obviously, trying to replicate the Crisis arcs is a very ambitious aim for the DCTV canon. Destroying and reinstating a multiverse they only just introduced would also be counterproductive. However, a plot which uses elements of the Crisis arcs is definitely possible, especially when it comes to Earth-Two.
There are already hints in The Flash that a version of the Justice League exists in their version of Earth-Two. So far, there doesn't seem to be any hints of Superman or Supergirl's existence in that world, but they could be in hiding. However, Hal Jordan, Diana Prince, and Bruce Wayne do seem to have teamed up...
A possible Infinite Crisis arc could ensure a crossover between all the DC TV shows, introducing Power Girl as Earth-Two's Supergirl, and explaining the apparent Justice League in Earth-Two. Considering the Easter Eggs and hints dropped by the show so far, it seems possible that the producers are already planning a similar epic crossover event.
And of course, there's the Legion ring in Superman's Fortress of Solitude, which we saw in Supergirl Episode 15. The Legion of Superheroes exist in the 30th century, so Supergirl could also be building towards a time travel plot.
Until we get more than hints and clues in the respective TV shows, all we can do is speculate. But both The Flash and Supergirl both seem to be building towards epic plotlines, and now that the multiverse has been introduced, the possibilities really are endless.