To preface this, this is a theory. I'm just here to pitch the possibility of a scene in which the Man of Steel could return to Earth to fight Darkseid alongside the newly formed Justice League of America in Justice League Part One.
So to start, the dirt on his coffin at the end of the movie is important. For all intensive purposes, he is alive, but barely conscious. Let's call it, for lack of a better phrase, a Kryptonian coma.
So Batman, realizing that if there is any chance that Superman is alive, exumes his body and brings it north to the Fortress of Solitude. Seeing that Kryptonian technology does have the ability bring back those who've died (Zod into Doomsday, except not a deformity this time), Batman tries his hand at Kryptonian genesis. Bruce, who also knows that it took foreign genetic material to complete the process, gives his own blood...no luck. But he does remember the warning of Earth 2's Flash from his "Knightmare". "It's Lois! She's the key!"
The grieving reporter is brought north. She, who was his world in life, gives to him her blood. Sure enough, the process starts. But at this moment, the invasion starts, which causes the JLA to spring into action, leaving Lois behind to guard Superman.
Midway through the battle, as Batman regroups the team after the first day of combat. We see the Fortress once again. Lois is watching the horizon out in the freezing cold, awaiting the Justice League's return. When suddenly, almost echoing the shot from Man of Steel, the doors open into the sunlight. What Lois sees, is a lone figure in silhouette, his dark red cape flowing in the wind. She smiles, and we go to black.
I personally think this thread would work quite well on how to get Superman back into the DCEU. Maybe there's some science missing in my explanation, some story errors, or it might just be to cheesy for you. Whatever you think, let me know in the comments. Thanks for reading.