Correct me if I'm wrong, but I think Duegar were intended to be the drow dwarves originally (based on their coloring), given a couple spell like abilities to make them ambushers and able to surprise characters with giant size when they thought they were fighting dwarves.
So I think the flavor we all like about their society and culture came later as people tried to make them more interesting than that. It worked very well, but I don't think it is really contrary to their fiendish heritage. I think the closest fit would be the layer of Dis, because it is gloomy and Dispater in history was also known as "Pluto" or the lord of wealth. Dispater as lord of the city of the dead also works to introduce necromancy to the culture. The Duegar of Krynn (Daegar) are led by "Bonemasters" so it has been done before. Another fit would be the realm of Mammon.
Now about the Duegar psionics, I've always found it an awkward fit. I believe the origin of that was their racial enslavement by the illithid, but that runs the problem of cutting into the Githyanki's backstory and role in a campaign setting. So I'm fine with an infernal rather than psionic explanation for their racial abilities.
Finally, I find the most significant feature about the new Duegar I like is that they will have a variety of abilities. This means a more dynamic approach to humanoids and monstrous humanoids, in which the party can switch up different roles. For example, I imagine the Duegar defender will grow to giant size, while the Duegar striker will turn invisible, the Duegar controller stone shaping or blasting hellfire... and well maybe Psionics will play a role for the leader if they don't get rid of them.