There is no such "private key" owning the whole eth blockchain. You obviously don't know at all what you are talking about ...

The is some preliminary research on cohort adverstising ; https://www.adexchanger.com/pr... This is the kind of technology that would provide better privacy for everyone while still allowing big businesses from doing efficient online targeted advertising. With all the privacy laws being adopted evrywhere at an increasing pace, Facebook will have sooner or later no other choice that to adapt or disappear and be eaten by the competition. There will be a time when the amount of users on which they can freely scrap all data without consent will diminish. So they will have to take action to play by the rules of the majority and change their business model for good.