It will add online co-op voice chat, checkpoint saves, and the ability to copy saves. Because when you're surviving the zombocalpyse, you should probably make use of checkpoints and stay in contact with each other. The game has been out for over three months now, so we wouldn't call the features timely, but better late than never.
The patch is coming on Monday, March 7 for your zombie hunting convenience. The blog also promises "further surprises" coming with the patch, which is a bit vague. Extra skins? New weapons? Zombie fashion mini-game? Your guess is as good as ours.