I thought this topic seemed familiar for some reason.

I looked back but didn't find that thread.
In any case, to spur new discussion, I think that the biggest possibility for a new victory condition is diplomatic. The UN was a poor implimentation in Civ 3, and there's many ways that it could have been done better.
In my proposal, each civ should have different categories of relations with each other civ. So, for example, each civ would have "trade relations" (how much they trade techs and resources), "ideological similarity" (in case they have the same religion or government, for example), and "political cooperation" (alliances, ROP agreements, etc.). Each of these categories increases or decreases based upon deals between the two civs. If you have a military alliance, your political cooperation value will be higher.
The value of each category between all civs is summed up - so you would add up the "trade relations" value between Civs A and B and A and C in order to get Civ A's "total trade relations value." In order to achieve victory, each category would have to pass a certain amount as well as a totaling of all values for that civ (the threshold would be determined by how many civs were in the game). So if there were those 3 civs in the game, you would need a value of, say, 20 in each category as well as a total of 80 (20+20+20 + one more 20 in order to give each civ some leeway in what it concentrates in). So once you reached 20 points in each category and a total of 80, you would win the game.

The total amount of points that each civ has in each category should be available to all civs (perhaps it would require an embassy), so you could determine how close each civ was to winning through diplomacy. If they're too close for comfort, you can act (attack them, cut off trading, etc.).