"Next up is the Free Roam Pack, featuring new Free Roam challenges, "action areas and defensive placements," posse scoring and leaderboards and the addition of new anti-griefing measures"
I can't help but think it'll be free just because anti-griefing measures seem just standard, they don't seem like something you should pay for.
The zombies thing though, I think it'll be very tricky to do right, but if it is done right it may end up being the next Nazi Zombies. Still, and despite my brother owning the game, I'll buy the pack.