This is what I found:
- Game originally called Call of Duty V. This can be seen on this image.channels, and green channel has highest definition, so, I combined it with alpha channel and saved image).
- Game featured training.
- There were 5 squad perks, first 2 were called All Seeing Eye and Commanding Squad Leader.
- Some maps were cut.
- PMD-6 mine appeared in multiplayer and could be placed using PMD-6 x2 perk.
- Select Fire attachment was for SVT-40 and STG-44.
- Fourth Killstreak sounds - B-17 Flying Fortress for USMC, Kamikaze for Japan, Katyusha Rocket Launcher for USSR, Carpet Bomber for Wehrmacht.
- Carpet Bomber was not only 4th killstreak reward for Germans.
- Game featured British campaign (the only known part at this moment is battle at Rhineland and Holland). Some of British weapons can be found in game: Bren, Lee-Enfield and Sten.
- Battle for Bloody Nose Ridge featured in game.
- Player could be banzai charger and banzai grenadier? (bonzai1 and bonzai2 textures)
- Cut game modes (Tank War, Vehicle gamemodes, Survival).
- Canceled, test or will-make-later Nazi Zombies levels (Zombie Theater and Zombie Coast. Probably third variant because Der Riese and Shi No Numa originally called Zombie Factory and Zombie Sumpf in localization strings). In maps files, there is code for Farm, Farmhouse and zombie mode Makin.
- American and Japanese tanks in multiplayer, especially on Beachhead.
- Grease Gun and PPS-43 originally were to be included in game.
- Code for strange level, Living Battlefield, can be found in game. As seen in comments in .gsc, the level is testing of some features.
- Overview of dogs AI test map can be found in game files.
I will expand this list every time I found something new in files.