And Halo zombies
And Far Cry zombies
And Borderlands 2 zombies
Okay, the others are mocking, but they really should make Borderlands 2 zombies.

or a battlefield 3 'zombies' not necessarily zombies but a survival mode,

*Cough* *Cough*Dinosaurs*Cough*

Holy shit... imagine like a jeep with 3 people in it trying to take down a giant raptor roaming Operation Firestorm... OR OR, Velociraptors in Metro

Dr. Zed DLC for the first borderlands proved that it was not fun to add zombies to the series

It was badly executed, in my opinion. Zombies should be like Mad Moxxi's Underdome in BL 2; long and/or endless waves, enemies getting constantly stronger, and anything similar that makes CoD zombies fun. Maybe even boss zombies inside rounds.
That could be fun.

Not every game ever requires zombies

If you want GTA zombies just go play either SR2 or SR3,
kinda the same aspect really.

no