I wonder if this crossover will eventually lead to the story that was hinted at in Doomsday Clock.

“On July 10th, 2030, the ‘Secret Crisis’ begins, throwing Superman into a brawl across the universe with Thor himself…and a green behemoth stronger than even Doomsday, who dies protecting Superman from these invaders.”

IMO this isn't the end of the Arrowverse. That ended when the final episode of Flash ended. Prior to the reveal that this show takes place on an Earth with no other heroes, I considered this part of the Arrowverse. Once it was revealed that it took place on another earth that removed it from the Arrowverse.