I like it! I reckon it could have killer multiplayer scenarios .... like allow for non-linear story progression ... like Stalker ... and have a Co-op online mode for the singleplayer ....
And have settlements rather than survivors ... like only having one or two survivors every square mile might heighten tension .. but having camps will make it feel more community-based.
*idea*
You could also have other fun things in the multiplayer .... like have a scenario where there are waves and waves of NPC zombies .... and its just you plus 16 other people in a roamable city block with a couple of underground bits and towers ... which you have to search through to get weapons....
So you can do the team thing and go together as a group, or if you're greedy and want that super powered shotgun spawn on the top layer of a tower ... you run off to get it before your teammates get the idea ....
And what happens is it becomes a battle royale like scenario ... like zombies are everywherem, appearing everywhere where there are shadows and so forth ... *IMPORTANT* and as soon as someone gets bitten they become infected!!! And they get to control a zombie each and every wave......
So if you get bitten and turn into a zombie the next round .. you can take your revenge out on someone on your team that left you for dead!! Lol
So each time a person dies ... it becomes harder and harder to win .... because you get more and more human controlled zombies as well as total zombie numbers...
And when it gets down to 5 people ... you can allow the human characters to teamkill each other .... so it becomes a mexican standoff like situation, like ... Blow off that zombie's head ... or shoot that pretty, young girl with the Mac 10 before she gets the same idea! But as soon as you kill another human player .. your position and your wrong doings are advertised for a shortwhile to everybody!! And you had better like the prospect of surviving alone and fleeing the zombie masses by yourself from then on!
oh ... and when you get down to one person, you have to get to a randomly determined location for retrieval via helicopter or some sort ... to stop campers from staying in the pickup location for the entirety of the online game.
Personally I would like to see how loyalties work out in a game like that ... like lets say you form a budding relationship with someone ... and you decide to link up together as you get down to 7-08 players strewn across the map ... but at the same time ... that niggling feeling in the back of your head is going off that they could be levelling their rifle at thge back of your skull waiting to pop a cap in it. Brrrr *shivers* spooky feeling
Or it could be that its just you and a friend and its down to 5 players total ... and both of you decide that you shouldnt waste your limited ammunition on eachother and just use it on zombies or players that are on their own ... and then the Mac 10 spawns infront of both players .... lol .... that'd be a killer scenario.
*end of Idea*
But personally I like your idea n.n