Well since this is in a sense a 'new' mod, I think it's time to bring up some old ideas.
First off, there is the basic zombie. Zombies infect who they bite, but I don't think units that survive a zombie attack should have a chance of becoming zombies since I'm sure the survivors have learned by the start of the game to kill anyone bitten by a zombie.
So, I'm not sure how it can be done, or if it can be done, but while a individual zombie unit may not have a large attack strength, there needs to be a way to boost it's lethality. I mean in normal Civ, a unit takes damage and then slowly 'regenerates' - well some of that 'regeneration' comes from previously wounded healing up and returning to duty. Yet in the zombie apocalypse, unless you are wounded by stepping in a gopher hole in the battle a wound is as a kill. So maybe the healing rate of units needs to be slowed way, way down. Anyway, I could go on about this, but I think we all can hash this out.
Secondly, specialty zombies: are we going to have them? I'm sure we can steal things like the hunter, tank, smoker, boomer and witch from Left 4 Dead. I'm sure there are other games that have specialty zombies as well.
Thirdly, at some point mankind gets the upper hand and the zombies become less of a threat and so each civ will start to look at other Civs as their primary enemy. I would think that for game play, instead of 'general' civilizations based on nationality, we should perhaps have civs sort of like Fury Road in that their 'nationality' is based on their leader.
In this I mean every group of survivors will probably center around a initial leader that sets the tone for their faction. Whether s/he Survivalist, Despot, Democrat (not the party; one wedded to democracy), Idealist, Green or what have you, each civ should have some sort of goal.
To start with, I think right off the bat, the initial factions should mimic those of Sid Meier's Alpha Centauri. I think it gives a good mix. Plus, I would suggest that each faction has a G/N/E leader like the Orbis Mod has.
Personally I don't like how most Civ games just end up a bitter slugfest toward endgame which is why I like FfH in that you have more special victories. Especially in a game like this with the zombies literally eating up most of the time till midgame, it would be hard to win a lot of the classical victory conditions like conquest. So I think each civ should also have a civ specific victory a la the Rhyse of Mankind mod.
And finally a note about alignments. I think they need to be seen in the sense of the game and not a value judgement on any real world beliefs. To me, especially in the sense of affecting the Safety Counter (if used) a 'evil' act or faction is one which a person today would consider such, regardless of it's actual 'worth' in context of the game. I mean being a despot who has his people take slaves would be consider evil by today's standard. Yet in game terms, it may be his civ that wins over a high-minded civ that ends up not producing enough troops and becomes zombie chow.
Anyway, the point is while the above despot might survive against the zombie, in relation to other human factions, there will be problems. Autocratic Generalissimos tend not to do to well with neutral merchants and high-minded humanitarians. I don't know, maybe we need to change G/N/E to something less emotive and more to something socio-political. Right now I can't think of anything. Something else to discuss.