A flip side of this is that I personally wonder whether Dark Sun can really work all the way to 30th level, because I'm not sure the relative mundanity of Sorcerer Kings etc can fit with the mechanical and fictional "heft" of epic tier PCs. It seems that it might work better as a setting that caps out at paragon. The general lesson (if I'm right - and I'm conjecturing, not talking from experience) would be that if you don't want your D&D to take cosmology seriously, and are going to focus on more worldly/mundane challenges, then recognise that and don't force your most gonzo elements onto that setting. (But then, to reference the other part of my post that you quoted, you better be prepared to make that mundane stuff sing, and I worry a bit that even 4e doesn't have quite enough to make that work - although I think [MENTION=6696971]Manbearcat[/MENTION] would disagree, if he's paying attention, as he always has interesting ideas - a lot better than mine! - for how to make skill challenges work for mundane physical/geography challenges of the sort that Dark Sun should involve.)
Nevertheless, I do agree that much of the appeal of a Dark Sun game lends itself to challenges that are most easily engaged and defined by PCs at the Heroic tier. I look forward, eventually, to finding out how these can hold their charm and develop further for PCs at higher tiers of play.
I too would like to hear [MENTION=6696971]Manbearcat[/MENTION] 's ideas about skill challenges for Paragon or Epic tier play on Athas, but I fear he is no longer posting these days....
On Dark Sun and Tiers:
1) Epic Tier is about cosmological significance/adventure.
2) The Dark Sun setting of Athas is cosmologically isolated. There are no Gods.
3) Inherently then, it would seem that Dark Sun Epic Tier play is incoherent. However...there are dormant Primordials (I believe). I think the question then becomes about the premise of the setting and the potential themes of an Epic Tier (and how they could bear cosmological significance).
We have Dying Earth as the backbone of the setting. We have a sun that is reddened due to sorcery. But what does that mean? Is the sun in a Red Giant phase like our own, ever-swelling and soon to extinguish all life? If so, maybe you have a modern sci-fi premise that could be worked into Dark Sun:
We need to find a way off of our dying planet/away from the impending exogenic or extraterrestrial extinction event.
So now the quest to undo the cosmological isolation and deliver the Athasian refugees from extinction commences! My guess is the Primordials wouldn't be pleased with that!
On desert-based (climate, topographical, fauna) threats:
a) lack of freshwater
b) intense heat during the day and intense cold at night
c) flash-flooding
d) sandstorms
e) dangerous fauna and territorial predators (this shouldn't be a problem for D&D!)
f) sparse vegetation and lack of game (food)
g) mirages
h) high mineral content (damages goods and drinking water with significantly high mineral content is a health hazard)
i) the fatigue-burden of traversing on foot through sand
j) lack of navigational landmarks
Then there should be plenty of fantasy-based dangers. I suspect there could be the equivalent of a desert crevasse covered by thick sand that shifts and pulls people underneath into the deep dark. Lightning sand. Etc.
All Skill Challenges need the context of a game to discuss in granular detail, but I think all of these threats can be amped up for Tier-relevance. Further, (a) and (f) need to systemitized in Dark Sun I'd think. The Disease/Condition Track is something that should probably be regularly attacking PCs (one for Exposure, and one for Thirst/Starvation). Surge-loss should be significant. Extended Rests should be impacted.
That is enough to start discussion.