It appears to me that 4ed is essentially already overloaded with options in terms of race. Each new player handbook adds several new races to the already expand basic list. This is probably where I wished they showed some more restraint and kept it to the same list of basic races to the original version of Dark Sun.
I just do not think Dragonborn, Eldarin or Tieflings belong on Dark Sun especially as PC races. They claim the Dragonborn are rejects from Giustenal but given the nature of the lone know Dragon the Athas, I do not think any Draconic beings would be welcome in the citystates. It is not like you are short of races with 8 in the classic version. So if I was going to run a game the allowed races would be Human, Halfling, Half Elf, Thrikreen, Mul, Dwarf, Half Giant(Goliath), and Elf. Revised Dark Sun added in Pterran and Aarakocra but I could take or leave either of those as PC races neither of which shows up in this edition anyway.
An important part of Dark Sun has always been that the classic fantasy races are present but very different in nature. This was done not just with changes in physical descriptions, dwarves are all bald and elves are tall, lean desert runners know to be thieves, but also changes to special rules or some new ability. In this edition, they just changed the flavor text but did not make any changes to rules. Seems like 4e has toned down some of the racial rules anyway but a rule change for each race would have been more interesting. Or maybe some new race specific feats just for Dark Sun. While the two new races have a couple of race specific feats and racial paragon path each plus 1 for half giants, the other races do not have any new feats or Dark Sun specific racial paragon paths.
They did not do a bad job with this section seeming to just take the easy route by essentially changing nothing on the basic races.