Henry Cavill had expressed interest in having Brainiac be Man of Steel 2’s main villain, and in the modern era, he’s usually connected to Krypton’s history.
That said, perhaps taking that kind of creative approach would have resulted in Man of Steel 2 feeling too similar to the Syfy series Krypton.
Perhaps Man of Steel 2 would have seen Superman departing Earth and going on an adventure elsewhere in the galaxy, as the DCEU has yet to deeply delve into its cosmic roots yet.