At the iZombie panel today at San Diego Comic Con, DCTV showed a five-minute video that was part-recap and part-setup for season 4. The third season ended with the world learning about zombies, and going into the next season, the city of Seattle will be walled off and the government will be supplying brains to the infected. The whole dynamic of the series changed in many ways and the show will be very different.
They couldn't roll out any new footage because the show airs starting mid-season for the CW, so the next season hasn't started filming. But what the lacked in new they made up for in volume. iZombie is based on the Vertigo comic by Chris Roberson and Michael Allred, it was adapted for television by Rob Thomas, and stars Rose McIver, Malcolm Goodwin, Rahul Kohli, Robert Buckley, David Anders and Aly Michalka.