Mad-Max style cusomized cars would spring up all over the place after the apocalypse given that working parts would become scarce. I am sure eventually some survivors would mount weapons on their vehicles and armor to defend against zombie hordes, too bad it would mostly be used for PVP in DayZ. It's a good idea, but they would need to take a lot more work to fix than normal vehicles. Edit: For future "standalone" speculation, modular vehicle customization? Customizing a bike with a minigun? Yes please! Also, bus with flamethrowers.