I’d like to think that zombies would be temperature dependent.
As temperatures drop, it starts getting harder to survive in other ways, so why not have new opportunities arise based on season?
So, summers the season of plenty, the wilderness has got all kinds of food in it, special warm season creatures like the giant mosquitos and frogs flourish, active zombies wandering the cities, giant bees gathering honey, etc.
The numerical thermometer on the hud should be removed, and instead various in character ways of determining the temperature, like thermometers or tuning a radio into the NOAA automated weather forecast service.
On that note maybe a new domestic bionic that connects to an automated weather satellite can give you current readings for your area, as well as the weather forecast. It could be pretty handy.
Winter could be a boon, if you are prepared.
Zombies get sluggish from the cold, and even freeze stiff when the thermometer drops below zero. Now, it’d also be hard for you to be out trekking in the freezing temperatures, but it’d mean that you could loot cities with some relative safety, as long as you don’t freeze to death, or the temperature doesn’t rise above freezing, thawing the zombies…
Also, I’d wanna see some abominable snowmen and yetis out lurking the woods, maybe new enemies made entirely of ice, giving new incentives for using flame based weaponry.
Just my two cents.