These already are in demo apps and projects on SAFE. “Impossible” is another of my never use words 
It is possibly to do this in a myriad of ways. Today somebody pays, usually the app supplier, that can still happen. In SAFE there are a lot of ways to also do this, i.e. read X things, get a credit (that pays the safecoin part) etc. App dev then pays, but the user increases the reach of the site and then possibly again when they post content. So monetise that directly and not in a hidden sell the user’s data type approach.
The issue/trick is using new tools to do things in new ways, not new tools to mimic old ways. The hope is some of these new ways are actually better user experiences than the current models. Privacy aside (much larger convo).
Of course another significant issue in SAFE is that publishing a site/app is actually global. So a dev in country X creates and app, now people in country Z do not worry that country X located servers/companies are sniffing data. Users may not care in some areas, but business certainly does. So cross border data handling becomes a solved issue. That is also a huge driver and B2B is an enormous market.
Probably straying off topic now though.