The Dark Copula is an enormous dome of shadow that protects the Lands of Eternal Dusk from the rays of the crimson sun. Hindsight, I wish we made the dome a bit smaller, but it is what it is at this point.
My reasoning for including illithids ties back to the Black Spine adventure and the githyanki’s presence on Athas. My rationalization is they wouldn’t have built an entire prime material city without good reason unless it was to destory a large concentration of mindflayers. As part of my DS history I have it that rhulisti and illithids had a conflict at some point during the Blue Age. Illithid graft technology is very similar to life-shaping. For my DS lore I have it that the rhulisti unlocked the basics of life-shaping from “stolen” mindflayer grafts and illithid tadpoles.
My thoughts around a proto-champion is Rajaat wouldn’t have the Champion making process perfected on his first attempt. There were likely failures resulting in some horrendous abominations. Some mindless and others not so much. Its also a good lead in on how Rajaat discovered Champions needing to be accomplished in psionics as well as magic.