I just find Dark Sun out of all the classic settings to be the weirdest thing to add to a multiplanar game. From what I read on Dark Sun sourcebooks, the setting is specifically designed to be self-contained and breaks away from most of the classic D&D assumptions: There is only one dragon and spelljammer lore had previously mentioned it was not possible to reach Athasspace for reasons (if it wasn't that, I'm sure I read somewhere that World Serpent Inn had a door that opens to Athas, but it explicitly did not allow you to go to the inn through Athas so as to make sure that any hapless Athasians could not escape the torture that is their dying world). To take a setting like this that was explicitly cordoned off from the rest of the multiverse and add it to one of the 2-3 page world descriptions is... weird. Furthermore it really takes away from the hopeless post-apocalyptic feel of the setting. If old Dark Sun was Mad Max, now Max seems to have the option to hitch a ride on a spaceship and get away from crazy biker gangs!