Just to throw more ideas out:
The cinematics suggest the mind flayers are dying. There were already many mind flayers who were dying before the attack and crash. Perhaps the tadpoles is their last ditch effort to survive as a species?
That may require godlike power. And we know in Faerun, the number of worshippers increase the strength of a god. Maybe the mind flayers are trying to elevate their own god through tadpoles. Mortals have ascended to godhood in Faerun.
Yes! Even the first time I watched the opening I felt really bad for that lonesome mind flayer. Poor guy (really!). All his friends are dead, he has to take care of a whole ship on his own, the nursery, the elder-y brains in jars, escaping githianky and then fighting off all the devils and cambions who try to kill him on sight. Then he tries to VERY GENTLY mind control a bunch of fishermen to survive and gets offed for his efforts. Then he gets taken to a stinky goblin camp, his cadaver interrogated by people who clearly can't properly interpret mind-speech, and probably burned. If anyone deserved an afterlife upgrade, it's him.
I think that I like the idea of having different gods in each tadpole because the powers that you get are different depending on your class -- it's not a "one size fits all" murdery power, besides the "repulsion" one with Omeluum.
