I remember a thread about this being made on Bungie.net mere months before the game was launched so obviously few of the thoughts could be implemented. But we still have time. SO, I believe we should think of stuff to make Living Dead an interesting and unique gametype.
For example the zombies could have their own “undead” player models with damaged armor and broken helmets. Perhaps even make the zombies themselves flood combat forms as either the default or a gameplay option. “Undead” player models would use the sword while the Flood models would simply be unarmed and would use melee attacks that have the power of the sword. They would simply be awesome cosmetic looks instead of powerful flood forms. This could also lead to specialized zombie/flood gametypes for both fun custom games and even machinimas.
Maps made specifically for Living Dead maybe? Maps that CAN be played for regular multplayer but are made specifically for the gametype and all of its complexities.
Come on, we should suggest more stuff! Who knows what 343 might consider if we all support it enough.