You could use AI, but I think even smart contracts would achieve the same result. If a person clicks on the article, they auto-pay 5 cents etc. 

The biggest concern IMO is that we are looking to minimize friction between two users making micropayments, and I agree that zaps (for right now) are the easiest way to accomplish this. But zaps are running on an entirely unsustainable backend, where members of the blockchain offer compute to verify transactions. 

If the number of micro-transactions on the BTC blockchain suddenly skyrockets because of a new online economy which depends on this, would this even be a sustainable approach?

I am pro crypto, fiat currency is 100% not the way to go with this. Not even their centralized crypto which they want to push. But I have my doubts about BTC proof-of-work in a large scale economy, and the closest alternative ETH uses proof-of-stake yet is a centralized asset run by Buterin and the ETH dev team.

Am I wrong to question BTC on a much larger scale, and where is the POS crypto which is genuinely decentralized and optimized for frictionless micro-transactions?