There's no law of nature that data/eyeballs-based monetization (including advertising) has to remain viable everywhere that it is today. I find it entirely plausible that 10 years from now people will have to directly pay for more of the services that they use.

You're already seeing this with the increased number of paywalls around publication content. I expect we'll see more subscriptions and services just shutting down if people aren't willing to pay.