Ok here's an idea I've been breeding for victory conditions. Let me start with this: We all know the AI will never be able to compete against the player and have a possibility of winning - it's only good as an obstacle to prevent the player from winning too fast, or altogether. This is true for all victory conditions, even prestige points with the territory requirements removed (the AI doesn't do a good job of getting them it seems).
My idea is to accept this premise and therefore base the decision of whether or not the player wins the game on his performance - to be measured in prestige points. At the end of the game (there could be different lengths, maybe 30 years, 50 yrs, 100 yrs) the score is compared to a target set which tells you how well you did. The target numbers would depend on the faction you're playing and the difficulty setting - if you score too few points, you'll lose. The achieved scores could afterwards even be posted in the forums and players could compare them, like a highscore system.
To put it another way, the player wouldn't compete against the AI but he'd play as well as he could to meet a target. I think this would allow campaigns to be interesting throughout the whole game and remove the "meh I won anyways, no need to pay attention" problem that the game is very much suffering from in my opinion.
The exact scoring mechanism would have to be properly designed of course, you'd get prestige for technology, buildings, army size, protectorates, diplomacy, missions, etc. - there's a great deal of possibilities.
So what do you think about this?