Let's see....

First I would make it a world where it felt like a Final Fantasy title.

I would have a beautiful world map.

There would be chocobos roaming freely on the open map. Each area would be distinct. The world would have around seven major factions. Mages, monks, knights and dragoons, the old capital which is now a thief haven, the scientist, the holy grounds, and the wild kingdom. Names are subject to change.

There would be a school where white magic is taught openly. Young boys and girls are hand picked to be part of this privileged institution. White magic is seen as a gift and is hard to come by. Meanwhile there would be a sort of sin city type faction that recruits the rejects of the academy or cruel people to learn the dark arts or black magic. white and black magic, though both seem to have been woven from the same cloth, one is seen in a high regard while the other is looked at scornfully. The black mages, though not all would be bad at heart are seen as outcasts if they publicly display their ability. That would be the two sides of magic for the setting at least.

Monks would have a sort of Fabulesque feel to them. Men who believe that their first are the most powerful of weapons, they train day and night to perfect their bodies. I say men loosely, because of course there would be women among them too! I would like to incorporate a more Asian style for these monks. Like training under a waterfall and spiritual meditations. They have their own beliefs about religion and politics. They act on their own and do not bother themselves with the worries of the world like every other nation does. They are completely self reliant. I would like their domain to be reside high up in some frozen mountain type area.

The knight of sword and shield would have many branches and would act like the military as usual. The Dragoons would act like the police for the modern nations. Think about it. They patrol the world with their airships and if anything seems out of the ordinary they could jump down from them...uh cause that's what Dragoons do...jump! Their would be a station for the knights in every corner of the map. It would be interesting to note that where the knights go their outward appearance would change too. say a knight spends some time mingling with the monks, you would get a combination of the two to make oh...say a Paladin or if a knight infiltrated the black mage group he could learn to be a Dark Knight.

The old capital, think of the Midgar slums. This area has long been abandoned by any normal citizens and is now a den of thieves. Its survival of the fittest here, and there is a weakly built hierarchy. One thief would reign supreme, but it would be hard to trust anyone here and no sole thief's reign has ever last too long. It would be a King of the Mountain type of structure. The ninjas and thieves would be in this area. Ninjas being the good, and the thieves being the bad. That's not to say there wouldn't be situations where that perspective is flipped around though!

The engineers would have their own utopia. they would also act as the rich and snobbish group. Though they create many of the world's technology, they own share for a high price. The scientist and engineers make the world turn with each and every new creation. Scientist would act like the time mages of this game. Engineers would have a create function where if they find certain parts, they are able to make new weapons and other types of things for them and the party.

Of course there would need the be the crazy religious order hanging around. They believe in a higher power and old scriptures have marked the holy grounds as some staple of importance. That would be where the main church is located. I'm thinking that maybe these religious guys could be the callers of this particular world, but I haven't figured out how to work that in. Perhaps they summon holy beings like angels? And those that have fallen off the path of righteousness could conjure up demons instead? Maybe...

Then of course there would be the wild kingdom. Think The Veldt, but with a more jungle like appearance. The Wild is mostly unknown and not many people know much about it. On the outskirts there would be adventurers who have heard talks about treasures untold that are hidden within. The beast master would be the king of this jungle paradise. His army consist of every animal in his jungle paradise. Recently he has been interested in locating a mate, and there has been a jump in female kidnappings. I can see a Jungle Book type of deal for this area.

And of course there would be tiny villages and cities all across the world along with these larger factions.

I haven't though of any characters yet, but they would range from every faction to make the gamer see everything from each areas eyes.