It's been a while since I read up on Dark Sun. 15+ years or so.
Polishing up a bit on the lore with the new 4E campaign books, I am thinking that the races as factions may not be the best of ideas. Instead, they can be "acquired" through various technologies (i.e. Diplomatic, etc.) and as heroes. It also seems to make more sense to segregate the factions out into Defilers vs. Preservers from the very beginning, offering 5 unique factions of each.
For instance, the Defilers could consist of various Sorcerer-Kings (sovereigns), unique to their own political/governmental structure (city-states), which will then still offer unique tech trees. Just as a primer, the Sorcerer-Kings typically reign in a strict hierarchal manner, with templars, pact-holders, and nobility (as well as some other classes) being the only legal population who are allowed to be literate. This, obviously, will hinder their technological studies. However, since they are defilers, and do not care at all about the preservation of nature, they will be able to compensate for this with slave labor and quicker access to magic.
Preservers, on the other hand, would not necessarily be considered chaotic, corrupt, or evil. They would tend to rule with an even hand. Their numbers would be fewer, but they would likely be more educated and skillful. They take care in their magic usage, and ensure that it does not destroy the land. This fundamental belief would also parlay into their expansion on all levels, therefore it could take longer to construct buildings and research spells.
It would be an interesting mechanic and balancing act that seems to equal itself out on the surface.
Essentially, all "races" will have their own personalities, strengths, weaknesses, and access to very unique buildings, units, technologies, etc. For instance, Defilers would not object to holding an arena tournament to the death for the sole purpose of crowning a champion (population is reduced over X turns, however the player is rewarded with a hero upon completion. Defilers would also not be opposed to medical experimentation to further their cause, thus granting them access to unique races (half-giants? undead?) to build their armies with. Preservers, on the other hand, may discover and unite with a unique druidic order, who's sole purpose is to restore the land.
Population will not be solely based upon food. Water is a rare commodity, and it will be equally necessary to find sources of this for population growth. This will likely be represented in the same manner as food. Both excess food and water must be available before housing can be built.
Masterwork technologies could be studied as well. For example, aarakocra feathers or crystal spider silk could be required to weave into cloth armor for various masterwork cloth armor. Kank or cilops bone would be required for masterwork chain armor. And so on.
Ceramic bits are the primary currency, replacing gold. Clay pits and kilns would be required for income.
The list goes on, but the possibilities are endless. Athas was built for Elemental and vice versa.