In fact, there’s already an example of this in the DCU. Batman appearing in Creature Commandos is exactly this. They don’t know who is playing Batman yet, nor what the specific story of his film will be, but they know they are going to make a Batman film. Batman is out there. So that’s why that got a tease.

James Gunn says that the first screenings for Superman have happened, and they've been learning some key details from them. The director of the new superhero movie also admitted they weren't ruling out some small reshoots too.

Gunn said he's bringing key lessons in franchise building from his time at Marvel to DC Studios, with a strong focus on script quality over release dates and building a connected universe that still allows for standalone stories.