The player and companions only know about the tadpole because the Nautiloid crashed so the process was interrupted half way through.

Thats the gist of it one can infer, seeing how other true souls dont know and refuse the idea of a tadpole in their heads.

The vision you get from the Goblin warlord of Illithids in a circle, all united, something, something - could be a sort of religious ceremony - process of telepathic union with their new god, illensine ?
And that would be normal for Illithids since they are usually all connected and control by Elder brains - which in this case is their new God. Who is the Absolute.
Which may very well be the new trick the Dead Three are playing on everyone.

Im not sure but i think they have been reduced to having physical bodies again, so maybe they united to be stronger and are hiding as the Absolute - pretending to be the new Illithid God.
Trying to build a new and improved army.

Since the dead three will be involved in some way, i kinda wish Bane would take prominence this time around.