What with the popularity of rationalist!fanfiction, I feel like there's an irresistible opportunity for anyone familar with The Animorphs books.

Imagine it! A book series where sentient slugs control people's bodies, yet can communicate with their hosts. To borrow from the AI Box experiments, the Yeerks are the Gatekeepers, and the Controlled humans are the AI's! One could use the resident black-sheep character David Hunting as the rationalist! character, who was introduced in the middle of the series, removed three books later and didn't really do anything important. I couldn't write such a thing, but it would be wicked if someone else did.