You're mention of Mark's wealth actually brings to mind a point. A project like this can create greater wealth distribution as, instead of a few benefiting from everyone's data, everyone benefits from everyone's data.

Also, page 8 of the whitepaper provides a very detailed explanation of how the ecosystem eases data sale, and it goes far beyond the current categories of personal data being sold. A simplified explanation is that the app users download has all the features to monitor location, physical activity, internet activity, and more. It's up to the users to allow permission for the features they decide.