There's rumours doing the rounds that Rockstar are planning to pull the same trick that they did with Red Dead Redemption's Undead Nightmare pack, by introducing the undead to Grand Theft Auto V. YouTuber Chr0m3xMoDz points to a DLC-centric section in the game's code that looks for "SPZOMBIES", watch the linked video to see for yourself what he's talking about.
This comes on hot-on-the-heels of similar claims made recently on gtaforums.com. Obviously this is far from conclusive evidence that this DLC is going to happen, but it's a noteworthy development if nothing else. Would anybody be interested in playing a zombified version of GTAV?