I've updated my overview of races, namely adding a description of Dragonborn. This concept was solidified by the backstory of Gaerbin Drake, the Dragonborn Paladin who will be joining the group when available. I'd been tossing around the idea that Dragonborn would be desert dwellers, and reading Gaerbin's backstory evoked a lot of Egyptian imagery to me. I'm not sure if this was the intent, or if I just interpreted it as such since I was already thinking "desert." So Arkhosia is loosely based on the Egyptian empire, which will mostly be cosmetic (Arkhosian ruins, Dragonborn art, etc. will be reminiscent of Egypt).
I was unsure whether I wanted to stick with the default "canon" backstory of the Dragonborn ruling an empire called Arkhosia, but I kept Bael Turath for the Tieflings so why not? The main difference now is that in the default Points of Light setting, Dragonborn are a common race, whereas in Talamhlar they're rare. I may also develop a connection between Dragonborn and Yuan-Ti (perhaps the Yuan-Ti took control of the former Arkhosian territory?), but I'll flesh that out when (if) the party gets to Paragon.
Despite the fact that during large chunks of the year the group may not be able to get together, I would like to run the campaign at least up to mid-Paragon (I have an aversion to the concept of Epic Tier play, so if the group makes it that far then the PCs will be retired at some point in Paragon).