Okay, so we've all seen the episode Trial of The Flash and a certain Earth was name-dropped by Harrison Wells. EARTH 15!
The Flash, Killer Frost, And Vibe try to contain the explosion of a Meta-Human and Wells tells Cisco to vibe a breach to Earth 15 because it's a DEAD Earth! According to the comic Earth 15 is a dead earth because Superman's evil doppelganger literally destroyed it and took over. So Superman Prime could exist in the Arrowverse. So fans are theorizing this could be a potential plot for an upcoming Supergirl and Flash Crossover as they have annual crossovers with each other each season. This time it could involve Team Flash and Team Supergirl. What do you think? Could this be the setting of the next Crossover?
Incase no one knows Superman Prime, he's the evil Earth 15 counterpart to Superman. He's basically like a Worldkiller and apparently, he went crazy and killed all the members of the Justice League and JCA and now Earth 15 is a firey dystopia