Let's entertain the idea that NWI decides to work on the single-player campaign again. These are just a few ideas up for discussion that i think would be a welcome change.
Exhibit 1: Health System
Granted, the TTK in Insurgency is its most distinguishable feature. For multiplayer this is passable, but for a full story campaign, i don't see it working without a few tweaks. The main reason being that instead of a multiplayer match where you respawn, we're talking about a campaign that may force you to restart at a checkpoint every time you die. For this reason i propose that, for the campaign only, the health system be tied in with the suppression system.
Basically, the more suppressed you are and the more foggy the corners of your screen become, the higher your chances are of getting hit. The damage output is still the same as multiplayer, meaning you can still very well be killed in one hit. Shots that don't kill you may still leave you weak and susceptible to a follow-up finishing shot. Therefore, along with ammo boxes and magazines being scattered across the battlefield, medkits should also be commonplace to restore the player to full health.
Exhibit 2: Story
My suggestion for the story involves the Security forces being contracted to fight for the local government of an as-of-yet unnamed Arabian country who claim they have been targeted by Insurgent forces of a neighboring country who had recently bombed several ministry buildings. In the name of the fight against terror, the unnamed Arabian country contracts the Security Forces to assist in their fight, sending them to fight alongside their own militia. The Insurgents deny any involvement in the attack and are forced to fight when their homeland is annexed by the unnamed Arabian country. The Insurgents then mobilize to defend the major sources of capitol in their homeland: It's oil fields, reserves, and farmlands.
The story will be told from the perspective of the player's own Security and Insurgent characters, alternating between the two every other mission.
These are just some of my ideas for a campaign. Free for debate and discussion.