Implanting tadpoles into PCs on Seadeeps
My players escaped Alterdeep, and then escaped (with many of the other held NPCs) the Mindflayer colony heading north. While the Qualith doors gave them trouble, and they met some githyanki scouts who are hightailing back to the Creche to report that the Illithids are weakened (only to find the chaos the party caused on THAT level), they encounter the Neothelid.
I am considering having the NPCs and most of the PCs implanted with a tadpole. The Neothelid avoids those (ala Ripley and the Alien in Alien3) implanted and attacks the ones that didn't "take" (i.e. one is a shapeshifter, etc). It will actually defend the implanted ones, and fight the ones that are not. Knowing the party, they will fight it regardless. Then, following a long rest, they may develop a psionic ability (with a DC check that will progress from 2 as they use the ability(ies)). The Ultharid will visit them somehow (messenger, dream, telepathy) and warn them to return to the pods for their own safety (it keeps the tadpole from developing) and of course for his own nefarious reasons, in reality.
So, I am wondering, why was this not included in the original adventure as an option, nor in the Companion? Am I missing something from this seemingly awesome story plot line? Tell me what I'm missing - and yes, I know some rules are DM fiat in this process, and yes, I have played BG3.