How to make Call of Duty multiplayer the most dynamic and innovative multiplayer game ever

First, credit where credit is due: Treyarch was at least 50% of the way there as far as the general idea goes.  In Black Ops 2 the option was there to share your custom game mode recipe online, and to "like" other players' custom modes and sort by popularity.

Now remember back in 2012, MW3's year.  When the game mode Infected was introduced in the public playlist there was a real resurgence in the popularity of the game.  Modern Warfare 3 had its problems, one of which was its similarity to MW2 and players responded by dropping out more quickly.  However Infected was a completely different type of game mode and its introduction helped the game's popularity immensely.  Then the same thing happened to a lesser degree when Dropzone was added.  And there was a week or so late in the game's year when 18 player free-for-all matches were glitched in or hacked into the game and the same thing happened for me personally that week because the massive chaos involved in 18 person FFA was new and exciting.  It made the game fresh again.  The way to keep the game fresh all year long (or even better for two or three years) is to constantly update the playlists.  

Now I think someone who combines these two ideas can make their multiplayer game more interesting and dynamic than any game out there.  Outsource your game mode creation.  In order for this to work you have to put a zillion options into private match so that players can create modes that are not simply a rehash of existing modes.

Some basic ideas for options to include:

1.  Every game mode from every past Call of Duty should be included in private match to give as many starting points as possible
2. Rounds in every mode
3. Limited lives in every mode
4. Time limits
5. Score limits
6. How points are awarded for every mode (like in BO2 you could customize Kill Confirmed to give points for kills and for tags denied as well as tags confirmed)
7. Limiting loadout options, opening up loadout options (like BO2 having the ability to play with up to 17 points)
8. Customizing maps like the number and placement of flags, bomb sites and bombs
9. Customizing maps by creating simple barriers to block off areas

And there are a million other options needed to really make it work, too many to list.  And create an interface so that players can easily look through other custom recipes and let players share and "like" other people's recipes.  Some ideas would be a title for the recipe, the mode used as a starting point, and a brief byline/description all view-able from the menu system, and then selecting one recipe lets the viewer see the details of the recipe.

When the game is new, November and December, the standard modes are great.  Everyone is getting used to the maps, the weapons, etc.  In January start a community playlist.  Then at least once a month (even better would be every two weeks) the development studio can take the top voted recipes, test them out to make sure they work well, and put one or two into the community playlist.  Switch out the old ones with the new ones each month, and if one mode is particularly popular leave it in the playlist.  And when the game's main year is almost up in October put in crazier and crazier custom games like the 18 player free-for-all.  

The DLC season for Call of Duty is getting old.  I bet if you watch the player-count closely you'll see very little change with DLC releases.  I believe if you update playlists with new and interesting game modes you will see smaller drop-offs in playercount and from that an increase in DLC sales and possibly even game sales.