I think I will go for the safe (and boring) path: Miniature holographic projectors, that the zombie robots put in place once they catch a victim -it's a festival, after all, so people should be willing to participate and engage a little suspention of disbelief.
Of course it also means that the actual holos will not be ready until the late 201's, but I can live wth a festival than grows up in complexity each year -from a group of people in make up in 2012, to an entire horde of zombie robots that catch and infect victims, rains of fire, flying demons, landmarks and entire districts turned into hauted post-apocaliptic ruins via solid holograms, etc. in Season 3
Of course it also means that the actual holos will not be ready until the late 201's, but I can live wth a festival than grows up in complexity each year -from a group of people in make up in 2012, to an entire horde of zombie robots that catch and infect victims, rains of fire, flying demons, landmarks and entire districts turned into hauted post-apocaliptic ruins via solid holograms, etc. in Season 3