If WoTC intends to bring back the Dark Sun setting for 5e, I hope they mention how the Halflings of the Blue Age used the magic of the Pristine Tower and the Dark Lens to become the humanoid species of Athas' Green Age.The majority of humanoids in my setting (to include humans, dwarves, elves, etc) all originated with one race that the Ancients modified their DNA to be their servants.
Not @Minigiant, but, I'd take a stab at that. Major population centers should at least have one Dragonborn "community" of some sort. It could be an enclave, it could be a mercenary group, it could be something else. But, something. Anything. Heck, make it an embassy of Tylamanther, if you like. Saltmarsh did that with a trade enclave from Iuz run by a Tiefling. Perfect way to inject setting lore into an existing setting.