Sorry for the triple post, but I wanted to have this mentioned and not clutter up the 2 ideas. This isn't a good idea for Diplomacy II, so excuse me again for the clutter, but like I said, wanted to throw this out there.
1 concept I always wanted to try and impliment, but never had the ability was a "Fork in the Road" type idea. By this I mean, code in some events that might change the world. This jumps into the realm of science fiction, using many of the sci-fi archtypes of doomsday.
i.e.
A) Nuclear Holocost: Reforms the world, destroy alot of things, Tech Tree changes to the concepts in Fury Road, where humanity starts from scratch.
Trigger could be X amount of nuclear weapons used
B) 1984/Brave New World: somehow let civilizations "merge" forming super nations (like in the Next War Mod). Let everything just get stronger. Basically the Next War mod.
C) Terminator/Matrix: Upon discovery of a tech called "AI", this spawns a Civ (maybe called Skynet or "The Machines", that have stronger units then most of mankind, mankind must band together to stop them. This is more science fiction.
This tech can be eliminated from being researched if the Nuclear Holocost happens first.
Again, this doesn't pertain to Diplomacy II, just throwing ideas out there incase any of it does sound interesting.
Either way, I do think an event, like too many Nuclear Weapons used, should cause some catastrophic event (either everyone looses, or tremendous global warming consequences, etc..)