Admittedly, any scene with the Bat would be fan service, but it sure would be nice to see Ben Affleck again before he returns in The Flash.
Or what could be even more interesting is seeing the Dark Knight have an encounter with Savant, a Gotham City-based vigilante who has ties to Oracle and the Birds of Prey in the comics.
Of course, the Caped Crusader has comic book connections to a few members of Task Force X. Harley Quinn is clearly the first that comes to mind and, after everything the character has been through, it would be nice to see this seemingly more formidable Quinn go toe to toe with Batman in a brief Gotham-set scene.