That probly would be crazy complicated, but so worth it. My ideas:
NO Permanent Alliances, just huge friendliness bonuses with allies (I wanna be able to betray Italy as Germany

), so human player can do whatever, but computer players will still play their parts well. We need some events like Vichy France (uber-friendly but not permanently allied with Germany, so human Germany can betray and occupy them when they want to) and the Spanish Civil War, and the Anschluss and Munich Agreement... Okay, I think we should keep most of the events, but enable everyone to DoW whenever they want. As long as computer players' attitudes lead them to play their parts (Czechoslovakia attacked Germany in 1937 for me in Free Play

), but human players can decide when and where they war.
Could AI attitudes be tweakable through the XML for their leaderheads? How willing they are to get involved with you in a war, how likely they are to DoW on a friend, etc?