Okay. First things first, I haven't read any of the posts yet, because I wanted to enter this with a fresh mind. But this is totally my type of thread, and something I've been thinking on for some time now.
Your Challenge:
Let's discuss how to include 4E's core elements in Dark Sun. How do we include the cleric, the paladin, the dragonborn, the tieflings, the fixed balance between classes, even the new cosmology, and make them feel enough like "real" Dark Sun that they slip in smoothly, without changing the overall feel of the setting? (We should also probably discuss other races that we know/suspect are coming, like the gnomes and the deva.)
Cleric
Clerics are easy. We simply get rid of any reference to deities, and swap in elemental powers instead. Channel Divinity Feats could instead come from which elemental power (or paraelemental power, to add a bit more variety) you have selected. And, of course, there would be feats that would grant special abilities to priests of a certain element - as well as powers that grant an increased bonus depending on your chosen element. (I would think Fire would gain bonuses to attack-style spells, Earth to defensive, Water to healing powers and effects that grant saves, and Air to zone effects and buffs).
Paladin
Y'know, you could easily turn the paladin into a gladiator, simply by changing a few of the power descriptions and re-imagining how lay on hands would work. If it were my home campaign, that'd be the fix I'd opt for. However, were it a DS product, you'd want to add a whole new Gladiator class, meaning "fixing" the paladin would be a bit more difficult.
I'm tempted to make them desert warriors that have risen since the fall of Tyr (I'd assume 4e DS would be set some time after the previous settings, similar to how the Dragon/Dungeon version tackled the problem). Maybe Villichi-trained Elemental soldiers or something to that effect. However, paladins worship all the elements - They are the angry fury of fire, the healing force of water, the impenetrable bulwark of earth, and the centre of the purifying winds of air.
Dragonborn
The name is really the only thing that needs to be dropped - I mean, the Saurials are similar, and the Pterrans are already a PC race! I'd also change the inherent honour that seems to come with Dragonborn, and instead make them similar to the PC pterrans - good, druidic and fairly isolationist. Of course, references to the long-lost Dragonborn nation would have to be dropped.
Another option would be for Dragonborn to be a new race, bred by one of the sorcerer-kings (I'd go with Nibenay) and raised to be part of the army. And, of course, numerous Dragonborn have escaped their life of slavery and now oppose the Shadow King. I think it'd be kind of neat to have some sorcerer kings prefer to use Half-Giants as their honour guard, while others use the smaller but more flexible Dragonborn as elite bodyguards.
Magic
Magic in DS is dangerous, and built around defiling and preserving. It's a big problem with any conversion - how do you fit the new rules system around an important thematic element of the game without it seeming tacked-on?
I think 4e DS should do what the original set did, and simply keep the rules "off-screen" for the most part (in the original set, Defilers simply levelled up faster and automatically defiled land as they cast). I really think defiling rules should be simple - if you choose to defile, maybe you get a +1 to the attack roll but defile land within a number of squares equal to your tier (1 square for heroic, 2 for paragon, 3 for epic). And, of course, there could be feats that let you damage opponents within that radius. If you cast a defiling spell within an already-defiled radius, you don't gain the bonus, and the radius expands by one - encouraging defilers to move about the battlefield.
That is, of course, a simple set-up, and it'd need a bit more thought before I'd settle on it. I think preservers would need some compensating bonuses, but really, preservers should be worse off - the inherent flavour of the setting encourages it. Besides, preservers get some great perks - the Veiled Alliance, and the ability to cast spells and remain relatively hidden.
Tieflings
Blah. Blegh. And other grunts of displeasure.
I dunno. "Magic-tainted"? "The Defiled?". A race that has been twisted by magical "radiation" could definately work, and fits in with the post-apocalyptic framework suggested by the original boxed set (remember, the original book described mutants and mutated features being common on most of the PC races, though this was later dropped).
I would drop the fire resistance, just because it seems like it could derail a lot of adventures in DS (what with the ever-present sun beating down on the backs of travelling characters...)
Gnome
"Long thought extinct, some gnomes have emerged from hidden sanctums beneath the sand to set foot upon the blasted earth once more. However, they have been changed by their centuries of enforced solitude, and are now bitter and angry beings..."
Druidic Fey could work, especially if we set them up as defenders of areas of pristine beauty. They would be tunnelers and animal tamers that attack in guerilla-style to protect isolated oases and glades.
Eladrin
I'd simply lump Eladrin in with Elves, and merely mention that within the past century, many elves have tapped into the elemental nature of the world around them to run "through" holes in the material plane and emerge a short distance elsewhere.
Eladrin would simply be elementally-touched elves - sort of like the genasi, I suppose.
Other Races
I do think many races need to be blocked from the campaign setting. There shouldn't be large numbers of orcs, drow, gnolls, hobgoblins, goblins, warforged, minotaurs, bugbears, shadar-kai, genasi, goliaths, and so on. One of the great things of the setting is the fact that it was NOT a "kitchen sink", and I think any conversion that opens up that floodgate is embracing a very bad idea.
However, you should allow those races in - in small numbers. And for that, I think there should more emphasis either on the mutation aspect of the original boxed set, or introduce a story element that allows new races into the fold.
For the first concept, all of the new races would be strains of magically-corrupted mutants, with certain strains of mutation breeding true in small mutated societies. So, we have the drow, but there's a very small number of them, and they're located in only one region. Goliaths are just mutated Muls, and the sorcerer-kings have figured out how to repeat this process and are now experimenting with it to breed a new super-soldier race. And so on...
For the second idea, the idea would be that the Gray (a plane that seperates Athas from the rest of the multiverse) has faded, and now many travellers are coming from other planes. I'm not a fan of this idea, but it could at least allow players to introduce whatever race they want, without having to re-write the entire Dark Sun setting to allow for large numbers of drow or whatnot.
A final idea that could be a lot of fun would be to set Dark Sun 4e in the Cleansing Wars, near the end of the period. There are a lot of races, but many of them are being hunted to the point of extinction. The city-states are beginning to emerge, and the land is already a desert... it'd be a good way to run a 4e game, while staying true to the canon of the game.
