The fact that, even after applying all this technology and know-how, the ROI on ad spend is a black box with no meaningful metrics, and the spending vectors are based on sentiment tells me that advertising is not a safe long term foundation for revenue. At some point, someone is going to have to prove that the money is well spent.

Mathematically I don't know if it is possible to eliminate all returns from ad spend market wide. Then again, negative interest rates should have been impossible.

Every trend I see points to greater ad reach. AR + automated transportation means the web expands from your phone to your surrounding. Regulatory intervention could just firewall behavioral targeting and e-commerce in to existing platforms, making Google, Facebook, and Amazon far more powerful.