Imagine a new level "Der riese 40 years later", That would be so sweet with more rooms, pack a punch machines, guns, easter eggs, carachters, throwables, etc etc.
A map that starts small, but expands though the later rounds. Mabye the zombies break down a door or somthing. Or on a certin rounod Every door is broken down, So in the last WaW Pack you only needed to open two doors to get to the box, but at round say 15 all the doors get smashed open or somthing.