OK, I like to throw out ideas and think outside the box, and I am going to here, I think the trailer has shown us a lot and also not every potential twist. There might also be some deliberate misdirection and even more so me clutching at straws!
What if a twist is that Lex Luthors ultimate aim is to have his very own Superman. Picture the scenario:
He builds Doomsday to fight Batman, Superman and Wonder Woman, knowing the only way he can defeat him is by Superman sacrificing himself. The dead body of Superman is then resurrected using the same device that created Doomsday but secretly Lex creates a clone or clones of Superman. (But we do not find this out for a couple of films.)
To some extent we do not know the context fully of the Superman statue, it COULD be at the end of the film when everyone thinks he is dead. This could unite the rest of the Justice League and could also earn some respect from Batman. It also would allow Superman to return, as of course he would need too for the Justice League.
Another theory I have is Aquaman having a cameo.
Let's say they cannot defeat Doomsday, or they keep defeating him and he keeps repairing his damage, would it be inconceivable that Batman or Superman get in contact with him. (Probably Superman after his scene in MoS) and they ask him to keep Doomsday under water, a sort of Phantom Zone if you like. Or maybe Superman does get killed and Aquaman is the only person who can bring him back to life? (Maybe even hinting he did it before!)
My first post so be gentle! But would love to hear thoughts