The SKs having technology of some sort while the rest of the world is in the Stone Age would certainly help emphasize the class divide.
Maybe that’s where the psionic mutations come from. Some kind of alien tech from the Far Realm that the SKs harnessed alongside arcane magic, that gave off a strange radiation that warped Athas’s fauna into the bizarre state we now see. The nuclear power to arcane Magic’s fossil fuels. That would actually serve to tie psionics directly into the settings themes instead of merely being tone setting.
If you go by the published backstory, psionics predate arcane magic on Athas by millennia. The backstory goes something like this:
- Distant past: the Blue Age. The world is mostly covered in water, the sun is blue, and the only intelligent species are halflings (and maybe thri-kreen). The halflings know a little elemental priest magic, but their main claim to fame is life-shaping, or bio-engineering. The Blue Age ends with a failed experiment of some sort causing a Brown Tide that threatens to choke out all life, so they used the sun's power to destroy the Tide, and in the process changing the world. This lead to:
- About 14k years ago: The Green Age. The water recedes, leaving verdant land under a now-yellow sun. The remaining halflings mutate into "traditional" fantasy races. The mutations caused by the Rebirth lead to a flourishing of psionic power, which becomes the dominant power of the age. The books describe amazing wonders made using now-lost psionic techniques. This is essentially the psionic equivalent of the "ancient super-magical empire" trope that many other settings have.
- About 8k years ago, one particular mutant called Rajaat discovers arcane magic and experiments with it for a couple of centuries, discovering both the principles of defiling and of preserving magic. He publically teaches people about preserving magic, and secretly teaches a select group about the more powerful defiling magic. Among the defilers who also prove capable psionically, he chooses a handful of Champions to start...
- The Cleansing Wars, starting about 3500 years ago. and lasting a millennium and a half. Rajaat turns his Champions into nascent dragons and sets each of them on a genocidal quest to eliminiate one of the "lesser" races, leaving them to believe that he intends to make humans the only remaining intelligent species. This is basically what turns Athas into its current state. Eventually, they learn that his real goal is to then eliminate all humans and leave the world to the halflings, and the Champions turn on Rajaat and imprison him in a pocket dimension. The remaining ones then each claim a city to rule as sorcerer-kings, while secretly sending sacrifices to power the prison keeping Rajaat away. That's about 2000 years ago, and started the "modern" age of Dark Sun.
So basically, psionics is an old, established power on Athas. It was more-or-less the only supernatural power around for 6000 years before arcane magic was discovered. Also, at least at the time of its introduction, taking the step from preserving to defiling was not obvious, or Rajaat couldn't have taught defilers in secrecy. One of the adventures features a document from the Cleansing Wars where the writer describes figuring out the principles of defiling as a breakthrough and, IIRC, "putting sails on a ship". But it's eminently possible that such techniques have been disseminated widely enough in the millennia in between to make it easy to make the jump.
Now, I don't see this backstory as being strictly necessary for a
current Dark Sun, but I'd prefer it if they kept it rather than involving the Far Realm or the Dawn War or such things.
Ideally, for Dark Sun I would want psionics to use different mechanics than magic, because it
is fundamentally different. I recognize that that's a big ask, so I'd settle for something like 3e psionics, which more-or-less uses slightly reskinned magic rules but a mostly different spell list. 3.5e psionics also had the difference from 3e magic that it included upcasting to make powers stronger, which is now a basic rule concept in 5e, but I'd like to see it have a stronger role for psionics. For example, 5e spells generally just do bigger effects when up-cast, but I'd like 5e psionics to keep the 3.5e tradition of doing qualitatively different things. To use the obvious example, 5e magic has
charm person and
charm monster as different spells, but the psionic version would just be
charm and depending on at what level you cast it it will be able to affect different creatures. You could also have a
levitate that advances from
jump or
feather fall to the equivalent of
levitate and then to
fly.
Another thing that differentiates 2e psionics from magic is the reliance on active use. When you activate a power, that costs a number of power points, and keeping it active keeps draining those points from you. You basically
can't make permanent or even long-lasting psionic effects. This is borne out by psionic items, which are quite rare and all of which have intelligence – they need a mind to use psionic powers.