While I would like a some native NPC camps on the island, the idea of the surge pulling NPCs from across the face of the Hyborian world is a really nice one to introduce enemies from areas where there would be no real reason to see anyone from, like Khitai.
Yes, I’ve looked into the thrall spans and found the Amazons and Aquilonians- but you have this great RPG mechanic; you should use it rather than giving us the same old desert dogs and Lemurian remnants. (But at least we get to know where all those Lemurians ended up, since they certainly aren’t on the exiles map!)