Latino Review's El Mayimbe appeared on a podcast and says he is hearing that Brainiac will be the villain of the Justice League movie.
It's said that similar to Zod discovering the Kryptonian beacon and finding Earth in Man of Steel, that Brainiac hears the beacon as well.
It's stated the end of Batman Vs. Superman will have some sort of set-up for Brainiac, which will lead into the Justice League movie.
Brainiac has yet to be featured on the big screen, but was a part of the defunct "Superman Lives" movie, with concept art even created for the character, and Brainiac was even a part of a sequel to Superman Returns.
It's also said that Darkseid is now being pushed back until a later time.