For example a % score with something like this: "Trustworthiness", "Political activism", "Obedience", "Addictions", "Laziness", "Morality", "Extroversion" etc.
It will be opaque and derived from their "secret sauce" by scouring GMail, DNS queries from your IP, phone calls you made on your Android phone, stuff you bought and search for in Chrome and so on.
Some companies and even landlords check credit scores when you apply. Criminal records. Border patrol checks social account postings. Imagine having access to all non-public stuff Google and Facebook has.
I wonder if that some point they'd know people better than people know themselves at. I kinda experienced that with Netflix when I was a subscriber. It suggested movies that at first glance I wouldn't think I'd enjoy but the algorithm had figured me out enough that if I took the suggestion, it usually was right and I ended up liking the movie. It was a pleasant and creepy surprise at the same time.