Watching a Few Video's on Darkness Falls and a Crazy Thought For a Mod Came to Mind.

How do you acquire a pigeon? Does it need anything to live, like food & water? Will zombies chase it? Is it vulnerable to attack? How does it navigate the game world? What if the recipient is sealed up somewhere? Is your pigeon identifiable from others? Can a third party intercept it and see the message? Could you follow the pigeon to discover a rival player’s base in PvP? Would text chat be disabled so you have to use pigeons, and if not, why would you?

Lots of things are doable, but the first phase would be to iron out the design.