The dead illithid in the goblin castle says its a circle of elder illithid in a circle in absolute unity, absolute power. Theres a few other clues, namely the worms in everyones brains, but its either a great smoke and mirrors or its a group of illithid working, potentially without an elder brain, but using what is most likely a netherse artifact (hag when she tries to get rid of your worm says its wrapped in netherese magic and its far beyond her power - and her power is great) to shield the slugs until the mass invasion (shown by dead illithid with infinite nautilus popping out of deep space for an attack).

What is the problem you are solving? Does your proposed change solve the problem? Is your change feasible? What else will be affected by your change? Will your change impact revenue? Does your change align with the goals and strategies of the organizations (Larian, WotC)?