One of the scraps we have been fed is that Civ 4 will involve more techs and diversity in the tech tree, more paths to take to get to the future that dont have to mirror each other or be as complete to arrive in similar places far down the path.
What would happen if starting out you only have very mild cultural/national qualities and attitudes, but instead what really shapes your national culture is the paths you take dcwn the tech tree, right from the get-go? Cultural and religious techs you research help to make you a militaristic or industrial or commercial nation in time, and the benefits you get (workers working faster or whatever, only begin to appear as that trait becomes dominant in your culture.
The full traits (and benefits) as on/off qualities are not all granted to you at the beginning, and you cant possibly acquire all techs or conflicting techs along the way. You have to choose a limited cultural path through history which winds up giving you two or three distinct dominant national traits (on a continuum now--how dominant is my economic trait vs. my militant trait vs. my industrial trait--could conceivably be an equal mix of all three or strong in one or two all depending on which branches of the tech tree you pass through and which optional techs you take the time to develop. Some techs perhaps should not be tradeable at all if you want to acquire them.
Your choices ultimately shape you into a cultural class roughly...the closer you are in certain qualities to other nations, the better you like each other. The sum total of how similiar/different you are ideologically and culturally ultimately determines how much you favor each other or dislike each other. Conflicting techs could not be traded because you would not be capable of learning/assimilating that alien/own culture-violating knowledge without the necessary grandually-acquired foreknowledge needed to get to that different, conflicting place in culture. Any nation going a significantly different route might not be willing or even able to teach or sell you that tech. Youd have to have researched that path yourself or at least gone down that path sequentially over time along with other nations who would be in your cultural group and would be the nations willing to trade techs along that branch with one another. The techs you would be able to trade and acquire would have to fit well enough into your cultural/tech path. Your culture cannot radically shift except over a long time.
Not everyone could learn democracy, for instance, unless proper philosophical, politcal, and economic precursor paths were taken (or whatever would be deemed to be necessary exactly). Other paths and traits would not permit some nations to lead into democracy, nor to acquire it, just as there is no way in hell America is about to help create a nice western democracy in Iraq, which has thousands of years of cultural and religious history very different in thinking and preference to ours, religions being no small part of that. If you are militaristic, you might be more likely to wind up communistic or fascist in the long run, because democracies are bad for lots of aggressive militarism...which is why America probably cant continue to be a democracy as we have known it much longer if we want to run about under police state conditions of ongoing military operations for the next 50 years trying to control and shape the world to our convenience.
These are very rough ideas thrown out. Im just putting out the basic concept: building your nations strengths/traits/advantages over time is mostly determined by how you go down the varied branches of a much more divergent tech tree to acquire and strengthen them. Different branches would represent the development of the different qualities we now choose two of at the beginning. The degree to which you start out with traits could be debated. The way Civ III starts in 4000 B.C. with strong traits already chosen, really sort of cheats and gives the nations the national identity they typically wound up with at 1000-2000 years later at the least. Perhaps though if it were desirable to start out with certain strong traits, then it would be necessary to have different and incomplete options for where to go in your tech tree next.
One thing Id likt, and that is that this would help to remedy something I find kind of unrealistic and annoying about the game...all the rapid instant learning and trading of every new tech from ancient times on across the whole planet. There should be much greater diversity and omission in who has learned what over time, with no easy way to go back in fill in the blanks if you did not chose to go that route in the age it was dominant, sequentially. You might skip the feudalistic government and military system entirely in your nation, for instance and develop in a different way to wind up with monarchical and democractic government. Or you might wind up with dictatorship in the modern era out of monarchy.