Well, I'm just thinking random thoughts here out loud about the possible plot, so if it doesn't quite gel smoothly in this post, at least you'll know why.
Ok, the each side has one special unique star player. For the US it's Col. Burton, for China it's the Black Lotus, for the GLA it's Jarmen Kell, and for the Militia it's the Assassin. Therefore the storyline should probably revolve around the assassin trying to get 'the documents you've mentioned, by assassinating a high level Chinese operative.
Three possibilities come to mind. The first possible storyline is assassinating the Black Lotus and intercepting the documents before she delivers them to her superiors. A great race, if you will, against the clock as the assassin attempts to track the black lotus every move across the map, only to keep missing her by mere moments. Then toward the end of the mission the cunning assassin finally has his one shot against all odds at catching (killing) her an recovering the prize. The golden documents. In the end you either get her, or you die trying.
The second storyline would be that the Chinese Secret Police have raided the home of a prominent member of the Chinese resistance, and have discovered documents that could bring down the entire organization. Because of time constraints, in a desperation move the militia's assassin has been hired to recover or destroy the documents, and recover the resistance member before the information can be used against the the resistance. This could mean infiltrating a secret police headquarters / secret prison somewhere in China. (PS there is Chinese Secret Police officers in Worldbuilder. I've never messed with them though, so I don't know if they do anything good.)
The third possible mission idea is a mission called "The Final Four". A rouge CIA strike team has created havoc around the world against the US, China, and the GLA. During their reign of worldwide terror they cross paths with, and manage somehow to piss off the Militia as well. <insert fuzzy part here> Somehow, the militia's assassin finds out that Col. Burton, Black Lotus, and Jarmen Kell are all on the trail of the rouge CIA team and all some how, however reluctantly, team up to track down and eliminate this threat to all. Possible plot twist. Jarmen Kell is secretly trying to recruit the team, instead of trying to capture and kill them, and somehow turns on Burton and his 'team'.
One last mission idea that popped into my tiny little mind at here at 2am, but doesn't quite fit what your looking for, but may be a fun mission re-enactment of sorts of the old Chuck Norris movie Delta Force. For those young pups that may have never seen it. Here's a synopsis:
A group of Arab terrorists hijack an American airliner bound for New York City. Taking all passengers and crew hostage and diverting the plane to Beirut, the group, the pro-Khomeini New World Revolutionary Organization, make demands to the United States government that, if not met, will result in the death of them all.
As a compromise, the terrorists release the non-Jewish, women, and children passengers. The remaining hostages are transported to a militant controlled area of Beirut. Using a sympathetic Orthodox Priest, the Israeli Army Intelligence prepare an operation to free the hostages.
The U.S. quickly responds by sending in Delta Force, an elite counter-terrorism unit to rescue the hostages. Successfully infiltrating the terrorist compound, they rescue the hostages and flee to the safety of Israel on the ATW jetliner, before returning to the U.S on a C-130 transport plane.
Storyline from Wikipedia at:
http://en.wikipedia....a_Force_(movie)The big reason I think this one would make a real good mission is that the hostages were split into two groups. Some were kept on the plane while others were transported to Beirut. meaning that you have two separate rescue attempts to make. One in a city landscape and the other at an airport landscape.
What would be an interesting thing is the time element. Like in the movie, after rescuing the hostages in Beirut, Chuck Norris had to haul butt back to the airport with the hostages before the bad guy's reinforcements arrived at the airport.
So the first part of the mission in the game is to secure the hostages on the plane, and take out GLA forces at the airport. The second part would be to infiltrate the GLA controlled city and rescue the second set of hostages. Then against the clock, fight your way back to the airport before a swarm of GLA bees all driving fast technicals (or something), sting your happy butt to death.
And if you really want to play with some brass balls, include a hostage killed counter that will end the game if x number of hostages get killed because of your incompetence at hostage rescue operations. Muhhawhawhaa...
More later, me need sleep... Sleep is good... Zzzz....