Heres some ideas i came up with but some will be in the game for sure. Make the game 2 Discs? Single Player on 1 Disc and the other Multiplayer and Zombies? or even 3 discs so they have enough space for content (Xbox) anyways here goes (this is for the zombies portion of the game; menu)
Campaign (Fight through undead horde and try to uncover the story behind the outbreak, written by George A. Romero; i think that romero did the story for it in my opinion)
Co-Op Campaign (Fight through the Undead story with friends; expect a L4D-esc game)
Classic Zombie (Fight through the Undead Horde with up to 3 other players; hardened edition maps (all black ops maps) will be playable here; Carry on the Richtofen, Dempsy, Takeo and Nikolai story)
New Zombies (Fight through the undead horde with up to 7 other players; New Characters)
Versus Mode (Fight with up to 11/15 other players but be weary, the undead horde is trying to eat you; expect an Operation Racoon City Multiplayer and i think the versus will be on the multiplayer maps, just more undead and red or something)
Objective Mode (Save civilians and complete objectives, Undead Horde with up to 3/7 other players)
Monsters Mode? (Fend off Monsters not zombies with 3/7 other players)
Alien Mode? (Fend off aliens with 3/7 others)
Be a Zombie Mode (You have the lust for brains, now go get some; can be played with 3 other players on your team with infinite lives on the zombie team. Your health is very low from the start and can only melee. the 4/ 8 players on the human team must stay alive and only have 1 life except if revived; if all get downed the game ends, this is bascially zombie mode but youre the zombie instead)
I personally think that Alien/Monster/Be a zombie mode wont be in it but hopefully the rest is in it mainly the solo & Co-Op campaign/new/classic/versus and objective modes. Please 3ARC we know you can do it and maybe add the Monsters/Alien mode and maybe the be a zombie Mode. Try and add a Map Creator aswell please thanks (Maybe only for Elite Members to create and share with other Elite members? Hell YAH, sorta like Halo Forge Mode, and add host migration aswell and maybe theatre mode aswell)
P.S Add a Currency giver so you can give money to friends or alies
Update 1: Ranking System: A ranking system sounds good but not to unlock weapons but for titles, emblems and custom attachments for the PaP (for e.g. the PaP for ak74u is a Red Dot Sight right? for 4000 Cod points, seperate from the multiplayer cod points, you can change the red dot to a grenade launcher or holo sight) and you can buy custom zombie emblems unlocked through challenges and leveling up.
Friendly weapon pick up after death:
IF a team mate dies after bleeding out, you can pick up their main weapon regardless if empty or full.
Classes (Not for weapons, perks or attachments but features):
another thing zombies needs maybe in the new zombies mode (keep classic one as it is) is classes such as medic, assault etc... but all of them play the same except for a minor kick (Assault can spawn max ammos every 50 kills, medic can revive allies even after they are dead; only once every 5 rounds, gangsta or gunslinger; more chances to get a good gun from the box and bezerker; every 100 grants you a 5/10 rage mode simular to the PaP'd VR11 and dead islands rage mode, you are immune to zombie hits and can kill them easily via melee or headshots).