User blog comment:SlyGentleman/Zombie Redemption DLC/@comment-2034460-20100719095719

I was wondering that myself. It could be Jack doing the work there, after you complete the main storyline... Or possibly it could be something that would be inserted as a chapter of the campaign before John dies... Another suggestion is that it is a playable "flashback" of sorts. I remember one of those is Revolver... Anyway, Who knows. We will have to wait and see.