As the cover to Batman/Superman: World's Finest #20 promises, "Mark Waid returns to the world of Kingdom Come!" Created by Waid and artist Alex Ross, Kingdom Come explored an alternate DC future where a new generation of heroes and a misguided older Batman force Superman out of retirement. The new arc of the World's Finest comic teases the Superman and Batman of the main DC continuity journeying to this beloved Elseworld.
Source:https://www.cbr.com/worlds-finest-batman-superman-elseworlds-comic-wishlist/