Instead of idle speculation, I decided to knuckle down and make some more short-term, probably not great ideas.
I decided to turn off my flashlight and see how long it took me to get noticed. I wouldn't mind this becoming an actual mechanic, since it combines both stealth and the utter fear that these undead just standing around will rip you apart if you make the slightest move in the wrong direction. However, unless they are previously alerted to your presence, they just stand around. Even if you get really close and attack them. They just consider you non-existent without the flashlight. So, there is no disadvantage to sneaking about without the flashlight. Here is a few ideas I had on this.
When the flashlight is off, your view should be more limited, even out on the street. Like, 4x4 (You can add more or less) with the player in the center without the flashlight.
Zombies react to sound by investigating the noise. This could mean a door opening, a window breaking, etc. If they find a fellow zombie, then they ignore it. If they find you with the flashlight on, it tries to kill you. If you didn't have your flashlight on, they go closer. If the player doesn't go away, then the zombie will sniff you out and try to kill you, along with all the other zombies in the area.
If you get too close to an undead, they'll peg you aren't a zombie and kill you. If you escape the area, they will try to hunt you down for a while, then forget about you and wander off. If you come back, they notice you. Yeah, it is kinda meant to be like Amnesia.
Just a few additions to make sure that a certain way of playing isn't foolproof.