I think Batman would be back in nipples, and so would the other characters like Superman, Green Lantern, and Flash.
All the costumes would be rubbery,
miss casted actors,
and the whole movie (plot, acting, villians, and film style) would be over the top campy.
Think back to the cheesyness of the Mr. Freeze movie.
Seariously though, I think he would either try and bring back the campy and cheesy brightly colorful fun of the JLA comics from the past, or bring back the campyness of the old Superman and Batman TV shows, and movies. (yes, exactly, a live action Super Friends. But maybe not as widely liked as Superfriends.)
or
After becoming such a joke of the superhero movie would, he would go the opposite direction and make a ultra super realistic and dark JLA movie.
With more serious acting, action, storyline, and overall mood of the film.