Idea #1
Gundam 00/Red Alert crossover
This idea came to me after writing through chapters of my C&C and Gundam SEED crossover. What if Celestial Being did armed interventions against the Soviets, the Empire of the Rising Sun, and the Allied Nations from the Red Alert series? Now I know what you're thinking, how could a crossover like this work? Well that is a very good question; one that I can easily answer in a few paragraphs.
First and foremost, the events of Red Alerts 1-3 still happen, but with a few changes. The Empire actually repelled the allied assault from both the Soviets and the Allies and maintained areas in China, Southeast Asia, the Philippines, Taiwan, Nepal, and several islands in the Pacific. The Soviet Union consists of Russia (of course), Mongolia, Cuba, most of Eastern Europe, Iran, Iraq, Afghanistan, Pakistan, and other nations surrounding them including Eastern Germany; except the Middle Eastern peninsula, India, Turkey, Norway, and Sweden. The Allied Nations consists of America, Britain, Western Germany, Western Europe, South Africa, Mexico, Central America, as well as a good portion of North Africa and South America, and Australia. Areas like the rest of Africa, the Middle East, and other portions of South America are disputed territories or their own independent nations.
The Empire is the nation that first developed mobile suits in the Third World War; the Soviets and Allies soon followed with their own. Since then, the three super powers have undergone great changes to their mobile suit designs that lead us to the mobile suits used by the Union, the AEU, and the Human Reform League, plus the Steel Ronin and King Oni from Red Alert 3. But they still use many of the weapons that are used in Red Alert 3, including tanks, fighters, etc. So needless to say, the Gundam Meisters are gonna be in for one hell of a fight.
The orbital ring is still going to exist, and each of the 3 orbital elevators that hold it up will be controlled by each of the 3 Super Powers. Heaven's Pillar will be controlled by the Empire of the Rising sun, the one the AEU possessed will be under Soviet control, and the one in South America will be under Allied control.
Many of the HRL characters will be Soviet loyalists, but I may have some of them to be part of the Empire of the Rising Sun. In this time period, the Empire has decided to hold off taking territory and has allowed peaceful trades with the Western European nations (I gotta get Louise in Japan somehow!), but it's still got its eyes on claiming the world for its own as does the Soviet Union. Many of the AEU characters, including their mobile suits, will be part of the Allied Nations. But this is where things will get real complicated.
Since the African Orbital Elevator is under Soviet Control, I'm not sure how to proceed with the first chapter where Setsuna starts the first intervention. A lot of the characters will be from nations that each of the 3 Super Powers will have control over so changing their loyalties will be like juggling. So unless someone has a better idea on this I'd like to hear it.
Now the events of the first season of Gundam 00 will still go as canon, but it will have a Red Alert twist to it, including the use of other weapons and vehicles. However, when it comes to the point where the AEU, the Union, and the HRL decide to join forces to deal with Celestial Being, that's where things will get even more complicated. I'm also trying to decide on what to do with the Azadistan episodes, including on their use of mobile suits.
I have not seen the second season yet, so I can't make any moves on it just yet. But unless someone wants to use this crossover idea for their own, they are more than welcome to.