Dragonborn would be perfect for the oriental empire to the west of the Sea of Dust.
There is an Isle of Dragons that may be ideal, off the south shores of that empire I think. The empire itself I would use for Oriental Adventures, like Greyhawk's Kara-Tur. You should look up the oriental dragon species and consider giving these dragonborn the ancestry.
In the Flanaess, which is the name for the common region of Greyhawk, the dragonborn would be peculiar to me. Not that I don't want to allow any race and class if the player is attached to them, but Greyhawk is the home of the Steel Dragon who prefers to be in human form in the cities of humans. They often have children with humans, and these half-dragons are there already only they look mostly like big elves. They don't look reptilian, or have a breath weapon of their own, and introducing a dragonborn would kind of overwhelm a player of one of these half-dragons. They wouldn't feel as much like a half-dragon. In the Oriental empire, whose name I just can't think of right now, but it may have been Linn, the dragonborn might not encounter the half-dragons and it would be most fitting closer to the isle of dragons where some of their eggs may have produced a good number of them and then some left in search of adventure and so entered the rest of the world.
It would be nice to introduce them there first, or say that a dragonborn in the Flanaess is a traveler. I tend to say monks and other oriental classes are from there, too, except when portraying the brotherhood. A dragonborn would be a fearsome creature to behold, especially if the breath was seen or if they were outfitted with impressive armor and weapons. It's nice that so many of them are lawful good, too, so rumors would quickly spread that they actually were sent by the gods to help mankind and the other races. They could gain acceptance quite easily, but maybe in general people who have never seen them before will run away or attack out of fear.
Just some thoughts, out of hand.