Even if FB were to try this, I don't think people would trust that their information is not being used for other (devious) purposes or that there wouldn't be some ads in the future even with the payments coming in. Trust has to be earned, and FB, in my opinion, has dug itself into a deep hole on that front.

The only reasons I see some people who're concerned about privacy using FB are because there is no better alternative and it's hard to move your network out, even if it's only for specific circles of people in your life.