Then fix that. Don't introduce entirely new mechanics for the AI to screw up.
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Also a bad idea. Again, there is a company called Paradox that releases games like that. Go play Paradox games.
You know, I think you've got a good point. The current system really isn't entirely broken it just needs some tweaking. Considering the timescale, a system where you have to make a reason for war just doesn't work. You need to be able to react quickly to anything that the AI does.
I think what they should do is focus on the 'warmonger' penalty so that what defines a 'warmonger' scales according to what the other civs have been doing, their relationships with you and the other player, as well as how much personal interest they have in said wars. They need a system that determines how much each AI cares about aggressions against you and can easily pick a side in each conflict. An AI sharing a religion with AI X would of course be hostile to you for DOWing after X converts one of your cities, while AI Y with a third religion likely wouldn't care about the religion side of things. The same would work with city states merging together multiplyers of the various AI's relation with the CS as well as how close it is to their border(when you are liberating one at least).
For example, if Monty bullies or takes over a city state Civs that were allies with that CS wouldn't mind and may even get a positive boost with you for attacking their rival.
A civ like the Aztecs also shouldn't have the 'warmonger' penalty with you if they are a warmonger as well. They should instead see you as competition if you are close to them(in strength as well as being physically close to them.) There should also be a 'peacekeeper' modifier you gain by liberating citys/captured units. It'll make warmongers cautious around you and peaceful civs more trusting.
Instead of making a whole new CB system they should work with what they have. When an AI does something and approaches you and you pick "you'll pay for this" that should give you a small window when you can declare war without making the other civs feel you're over-aggressive. Of course they'd want to add in AI 'apology' screens for when they settle near you/send missionaries after they've agreed to stop to take full advantage of that system.
Another important factor would be distance. Depending on how close you are to each civ(and this distance would increase up until it affects the whole world late-game) should affect how much they care about what you are doing. They should care less about being allies with a CS far from them as well as on what wars you are in. Leader personality would come into this as well. Ghandi for example would be less than tolerant about wars further away while America would only care about their surrounding area(building off of how the US used to be an isolationist country)
That is what One World means to me, we need a diplomacy system where talks and trades affect the whole world rather than only those 2 countries who are involved. A world war should always be just around the corner giving you reason to ally and pump up those civs falling behind in the game as well as giving impact beyond the choice of ignoring/DOWing/denouncing your rivals in the late game. A runaway civ of course should end up with the whole world plotting against him, which would put the runaway human player on edge. You'd have to be constantly checking up on/bribing the AIs to keep them from grouping up against you. Much more fun than hitting 'end turn' for the last stretch of the game.
The AIs need to be declaring more DOFs amongst themselves and making big alliances to truly bring in WWI/II scenarios in the late game. When a 'Sorry for bullying your CS' message pops up late game you should be asking yourself "Is this worth declaring war over, I know I'm justified, but X's allies won't care and will likely attack me as well." Late game, choices like that should have major consequences on world diplomacy. It'll be your alliance vs. the AI's and you will never know for sure if the other alliances/lone nations in the game will join up with one side, sit it out, or help out one side in a more discreet way(selling s. resources/open borders).
On another note, I wouldn't be surprised if the announcement was still a few months out. If I were a game dev I know for sure I'd let something leak out early and monitor what the fans think/want/expect before anything is set in stone. If the fans like the idea it goes ahead, if not the 'leak' was a lie.
