I don't see the add driven free services for all system survive in the long run. Say they start by dedicating more funds (hardware & software) to matching offers to customers with more disposable income. Say the next step is to offer more elaborate services or options to customers with money. Say, some coupon trick, if you buy a product A-Z you get 24 months of service B which is a paid version of the free service that served you the advert. This scheme is already doable with dumb adverts and without hoarding personal data.

Its already that you send the poor person a 10% discount coupon for one box of chocolate and the rich person 4 boxes for free, a bottle of wine and a life time 10% discount. Why would the digital world be different?