As I mentioned IRL, another approach could be a gift the razor and sell the blades strategy. It would be less technically challenging to simply give away a lot of data on a public blockchain which is already totally transparent, but to put a higher price upon your attention. The data is used by advertisers to inform whether or not they want your attention. Putting a price on your attention is how you monetize your blockchain data, ultimately.

Other data which doesn't end up on the blockchain could be made available as a service. For example, advertiser wishes to find out X about me, they make a network request to my computer/phone, the software negotiates a price according to your policies, and if an agreement is reached, you send them your data. Part of that agreement would be an implicit or explicit NDA, but ultimately enforcement of the NDA wouldn't be possible by technical means.