Called “Elseworlds,” the crossover ended on the thrilling reveal that 2019 would see the shows tackling the legendary DC Comics arc called “Crisis on Infinite Earths.”
That changed with the 2018 event that brought the heroes of Arrow, The Flash, and Supergirl together.
Arrow-verse fans have been able to rely on a big multi-show crossover for the past several years, but it was usually a long waiting game after one crossover ended before news of what the next crossover would be about.