Happy to see the mod is being updated! Haven't played the mod myself, but I've seen a couple of videos. I look forward to get the future A13 update and enjoy it myself.
I have a couple of suggestions about what I think would make the mod even more enjoyable, if the author doesn't mind.
(Keep in mind that I don't know the Rimworld scripting limitations, so I don't know if what I suggest is possible at all)
About zombie presence
I see the current spawning system used is a modified Raid. To make it more interesting/dangerous, I'd use a different way.
The idea: Define a "MaxZombiesInMap" threshold and keep spawning one/two wandering zombies each X days to reach it.
Why: Keeping a minimum amount of zombies always around would increase the overal tension a lot, and the delayed but steady supply of zombies would accurately emulate how zombie populations work. They aren't organized groups, but an inmense group of random individuals.
Going out for resources would still be possible, because of the delayed spawns. Players would wipe out the current zombie population and get to the resources as quick as possible.
The idea: Different seasons/events could modify the MaxZombiesInMap threshold.
Why: Things would be even more interesting if the mod took into account some of the vanilla events, like Cold Snaps, Toxic Fallouts, etc. This would make the experience a lot more dynamic.
The idea: Events. Big groups of zombies wandering to your area (not raiding you directly). A survivor trying to get to your base, chased by zombies. A strong wind that disables the Zombie Virus for a few days. A pawn contracting the virus randomly. A team of soldiers sent to your area to wipe out all zombies... and your pawns, just in case they are infected.
Why: Why not?
About the zombies themselves
The idea: Make sure that, if one zombie is attacking a pawn, nearby zombies enter combat too. Zombies should be able to comunicate when there's prey to others.
Why: Zombies should be aware of their surroundings and know when it's time to attack. This mechanic would help with that. Also, if you were to implement the "Zombie presence" above explained, it would help trigger massive attacks that would replace the current "Raids".
The idea: Zombie animals could be a thing. Either bitten or reanimated.
Why: You would be taking advantage of th Rimworld's natural animal spawning system to dynamically spawn zombies. Also, different locations would bring up different dangers, as there is a big difference between a Zombie Bear and a Zombie Squirrel.
The idea: Zombies always reanimate, as long as their brain is not destroyed.
Why: Losing is fun. Also, it would allow for interesting situations, like a zombie reanimating for the third time without jaws, arms, and having broken feet. Each time they reanimate, the damage from the last kill would make them more and more inefficient, so they wouldn't be as much trouble as the first time.
The idea: Buried non-zombies would have a small chance of reaminating every X time.
Why: Apart of the "dead raising" feel, this would make burying your people still somewhat dangerous. Bonus spook points.
About the pawns
The idea: Your people would get a negative mood for seeing a zombie.
Why: This way, the mod would poke into the Moods feature of Rimworld!
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Regardless of these ideas, I think the mod in its current state is awesome. As everyone says, take your time, Justin!