The reason why cookies worked so well is that the user didn’t have to do anything. Just go to a website, log into a social network, and your actions will be automatically tracked.
The ultimate solution for this post-cookies demolition man type of world is zero-party data. In some contexts, the user is willing to proactively share his preferences, in exchange of, for example, a better experience.
It is not necessarily a bad approach. It will require us as advertisers to redesign our buying experiences. You can’t ask the user, “would you like to see relevant ads related to your last purchase?”
This 100% opt-in approach also means the reduction, or destruction, of the interruption ads: because data collected for targeting will become less accurate now, the first ads won’t have the same impact as they used to.
This would lead us to a recommendation engine type of ads, where your advertising budget will only have a significant return if the user went through the purchase/subscription process first.
The money will shift to branding and building communities, and rely on people’s word of mouth to bring first-time customers.