Theros is even more limited in Races (Humans, Centaurs, Satyrs, Minotaurs, and Leonin, no other PHB options.
Class options are less restricted, as that fits the Magic Settings.
The point is, WotC has shown a willingness to limit options for a specific Setting, and nothing in Dark Sun would seem ludicrous.
Obviously I haven't seen Theros yet, but I hope you're right, and it's a strongly-worded limitation (which obviously any individual DM can rule 0), because the "limitation"
@Urriak Uruk quoted from Ravnica is not a limitation at all, but rather a mildly-worded suggestion that some races might be more or less suitable (and doesn't appear to limit classes/subclasses at all).
As people are saying, Dark Sun needs something vastly more severe, something that clearly lays out that by default, no non-Athasian races should be present, no normal Cleric subclasses should be present, certain spells should be absent, and so on. As I said, in a later DM-oriented chapter they can have a paragraph on flexing this, but the entire setting should be designed on the basis that it holds true.
Starting in 3e, thri-kreen became more humanoid in shape and it's always rubbed me the wrong way. As a point of comparison, here is what I (and many of us) view as the definitive image of a thri-kreen.
They're mantis warriors, not Star Trek walk-ons.
100% agree. They're mantis-beings, not humans with bug-ish features and maybe extra arms. That DiTerlizzi one is really good. They need to have an abdomen and a totally non-human physique. A lot of the more recent stuff for them just makes them look like 4-armed, vaguely insect-headed humanoids who have a humanoid torso (rather than a thorax and abdomen separately like an insect), and don't even have a real exoskeleton, just bony plates on top of relatively normal flesh.
Given Theros is adding Centaurs, who are far more extreme, this surely cannot be a real problem to do either.
