Although I don’t think the Mindlords need RMBs (for the reasons I gave on the thread concerning them), I like the concept of RMBs. To my mind the Illithids should have had much more involvement with Athas in the distant past. The githyanki city of Yathazor is too great an undertaking to simply be about dominating a chunk of an obscure Prime Material world IMHO. One thing guaranteed to get githyanki going is their ancestral enemy.
Anyway, tangent aside, abandoned illithid settlements and bases would make great adventure sites. There’s also the question of whether the illithid had any interest/link with the lifeshapers of the rhulisti given the organic basis of some illithid technology.