I don't agree with the "no fey" thing. Since Dark Sun has always had "Spirits of the Land", druids and their ilk, I think *some* fey, tied to the few green oases of the Tyr region, could work. Specially since you could have fey that looked like the Tooth Fairies from Hellboy II (think flying piranha).
Well, 4e is exception-based rules, so if the rule is "No Fey," the exception is, "Except for those rare sacred oases that Defilers have never touched."
I think the assumption should be that the PC's won't be coming across an oasis like that, and if they do, it should be an anomaly. No PC should be able to look at that and be jaded about it or familiar with it -- this is high weirdness. The feeling of grass beneath your feet shouldn't be a sensation that many have experienced before.
To help reinforce that, DS shouldn't have a real Feywild connection, not enough so that PC's are from it, not enough so that low-level monsters are from it. But note that I did point out that not all fey are inappropriate. Instead of the Fomorians being from the Feydark, they're from the Elemental Chaos. The tooth fairies aren't from some inscrutable magical Otherworld, they're a natural creature that has adapted Athas as a homeworld. Spirits of the land, sure, but these are
elemental spirits of raw physical power, not ethereal dancing sugar-plum fairies.
And Half-Elves wouldn't be "between two worlds" in a positive sense, but in a negative one, shunned by both sides of his heritage. OTOH, they'd make perfect Dune Traders.
Positive or negative, Athas is not a good place to be "between two worlds." The elves are specifically very xenophobic, and the blending of an elf and any other creature should be so rare as to be truly exotic. Again, no PC should expect to be that. With the archetype in general, DS is a place of very definitive strength, from my understanding. Someone who is in a state of being between things, with several small strengths rather than truly definitive power, is naturally selected against, to the point where they would become extinct. Or at least not encouraged as a race common enough to warrant an entry in the player's guide.
The perfect Dune Trader archetype, in my mind, is just an elf -- a swift runner who covers long distances and has, for one reason or another, lost the insular protection of the tribe. This establishes a community of "outcast elves" in the setting that the PC can belong to or liberate or otherwise work with. This makes an insular race more suited for PC's (because they actually do go out and encounter foreign things).
With the Fey and the Half-Elves and the like, it certainly isn't that you
can't have them. It's that they're
generally inappropriate (from my understanding). And they're also unnecessary. Thus, they don't need to be encouraged with an official page or so devoted to them. Devote a sentence to speculation in an "Importing New Races" section if they feel the need to address it at all. But I don't believe it needs to be addressed. The default question for someone wanting to be an Eladrin or a Half-Elf on Athas should be "Why?" It's like playing a happy-go-lucky tinker gnome in Ravenloft. You're missing the point. You should be encouraged to play something different. Don't try to fit the square peg in the round hole, just get a round peg.