One of the reasons I wrote the OP was that while "Psionics", broadly speaking, are important to Dark Sun, Psionics is not the same as having a psion class. Psionic themed subclasses and monsters, plus a boon-style Wild Talent system, are far more important parts of psionics to the setting. For me, Psionics is that gladiator who "cheats" by telekinetically retrieving their disarmed weapon. Psionics is the Psurlon that lurks in sand street. "The masters of the way" are... not actually that important to the function and themes of the setting. Sorcerer Kings and their templars rule over the city states through arcane, defiling magic. Yes, they also had access to psionics, but in 5e terms that's just some pionic-themed spells like Mind Sliver or Telekenises or Synaptic Static.
Dark Sun has other themes that would be important to address - restrictions on races, reflavoring & reframing classes, survival rules - but those all seem very doable in a 5e XYZ's Atlas of Athas based on what they pulled off with Van Richten's