It's not Superman, I really don't think so. Green Lantern hopefully. Superman will return in the film, but it'll be a total surprise to everyone in the film when it happens. Alfred specifically says 'you said you'd come' - now unless Superman called ahead or pinged him over an email to let him know he was on his way, then it wasn't Superman at the end of the trailer. It was someone Alfred had spoken to at some point in the film, I'm hoping GL, they referenced the Green Lanterns directly in the trailer and they're doing another GL movie.