“Throw Me a Lifeline” say’s Undead Labs as the next major expansion for their State of Decay title is currently in progress. The second expansion pack is titled State of Decay: Lifeline, which has no final release date as of yet! That’s a “YET”, so just have some patience!
Quoted by Undead Labs on their blog:
We are just now digging into the internal playtest process (which is how our favorite stalkers players on Steam found out about the title a couple of days ago – with PC testing, we are playing using Steam, so we can experience it the way you do). We’re not yet ready to discuss features or make promises. All we can tell you is that it will offer you a new way to play your favorite survival game, that we intend to launch on PC and the Xbox 360 at the same time, and that yes, it will broaden your horizons by a few kilometers.
The next update will bring with it a whole new map too, but no further comment was added other than the tease of new content.