I was sitting around shooting the breeze after the game today, and listened as my GM waxed poetic with regards to the first edition version of Oriental Adventures. I have had several opportunities to purchase it in the past, but passed each time as it just seemed like a gimmicky expansion set in a culture I wasn't familiar with. I'm still not entirely convinced I was wrong, but he's going to lend me the book, so I'll have the opportunity to find out for sure.
The main thing that caught my attention, though, was the concept of honor. I'm still fuzzy on the details, but if I understand correctly your personal honor is tied to your family honor, and your actions affect your honor and the honor of your family, which has real in-game ramifications. I'm very interested in looking at the mechanics for this, as it seems similar to what I'm going for here.
One of the things that I find as I play with different people is that some people will only be as invested in a game's story as they want to be. You can spend a year writing an intricate, complex back-story for your game, but it won't mean anything if your players just want to power game, or if they're just looking for a combat simulator. If you want to get any mileage out of having that beautiful back-story, if you want your players to care about it, you need to find a way to make it matter to the running of the game.
Myself, I play for the storytelling. Whether I'm GMing and telling the story to the players, or playing and telling my character's story to the GM, it's the drama, the characterization, the interaction with an imaginary world that drives me. I play with a guy, though, who is all about building the better mouse trap. He min/maxes his characters, works the angles, tweaks the attributes, skills, equipment and abilities so that if the dice roll right, he can drop that 300 hit point green dragon with one shot.
So how do I invest him in my game? How do I draw him out of that mindset and get him thinking about characterization and motivation rather than modifiers and bonuses? I want to cast as wide a net as possible with this game, rather than create a game that he (and others who don't share my specific goal set for roleplaying) won't be able to relate to, but at the same time I don't want to design for the lowest common denominator. Quite the opposite, in fact - if can do it right, I'd like to elevate the game, get people thinking and asking questions and discussing what is right and what is just and what is best, both personally, and for the society at large.
If the Oriental Adventures works the way I imagine it does, that may be the way - design a mechanic that ties the choices you make to those bonuses and modifiers. Make them care about how they act, invest them in the imaginary world, make them roleplay because that's where they find the angles to work.
Playing through Dragon Age on the X-Box, I admired the way they did the friendship/rivalry scale - throughout the game you have the opportunity to make smalltalk with your party members, and depending on how you interact with them, they either grow to like or hate you. If they hate you enough, they can even leave the party for good, but if you get them to like you enough, your inspiring nature (I guess) gives them cause to push themselves beyond their limits, giving them bonuses to their main attribute. If you want to, you can still go through the entire game without speaking to any of them once, but the game rewards you for investing yourself in the world that they've built for you, and while you may come for the stat bumps, you end up staying for the conversation itself.
Similarly, by tying the actions of the PCs to the development of the society as it rebuilds, I hope to eventually invest the players in the world itself. Even if they never move beyond the idea that they are being personally rewarded for contributing to the growth or downfall of civilization, they're at least putting thought into what goes on between the fights.