As it turns out, the Arrowverse "Elseworlds" crossover was actually just a prelude to a much bigger DC TV event that's coming: Next year will bring "Crisis on Infinite Earths" to the TV screens!
"Crisis" is one of DC Comics most famous and iconic storylines, and fans are using that iconography to create some great fan-made promos for this Arrowverse version of the story. Check out this "Crisis on Infinite Earths" poster, as created by fan artist, BossLogic:
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I avoided all spoilers to watch the whole #elseworlds crossover in one go like a movie. I got to say these crossovers are getting better every year, I loved all the comedy, Easter eggs, new faces, old faces, the lack of legend's made me a little sad. Everyone had mixed opinions on Batwoman @rubyrose I happened to like her, also just hearing batman being talked about made me so happy both badass. Everyone did an amazing job but my personal fav was Gangster Cisco (I'd watch his own show) Now this poster I made for last year's crossover makes more sense 😜
As you can see, the image BossLogic is invoking is the classic "Crisis" moment of when Superman is holding his dead cousin, Supergirl, in his arms. This moment occurred about halfway through the original Crisis, as the original Supergirl, Kara Zor-El, sacrifices herself in a do-or-die battle to stop the Antimonitor and his antimatter converter. Do to the nature of DC multiverse merges after the original "Crisis", Kara was erased from the new timeline, with only a handful of characters remembering she ever existed. Alternate versions of Supergirl were later introduced, and as a result of later "Crisis" events in the comics, memories of the original Supergirl started to resurface.
When has to wonder of DC and The CW couldn't be using the Arrowverse "Crisis" as a similar retcon tool - including using the original comics storyline when it comes to Supergirl. That show has been struggling to expand its fanbase, and could arguably be a series that DC and Warner Bros. TV potentially cut after the events of "Crisis". It would be a cruel end to Supergirl's story in the DCEU - but it would also be one hell of a big twist. The best part is that even if the Supergirl series were axed by "Crisis", the character (and actress Melissa Benoist) could still appear in other Arrowverse shows, as an alt-universe version of Supergirl.
The Arrowverse "Crisis on Infinity Earths" will kick off in Fall 2019.