Then again, there is some precedent.
Apple has said that hashed emails and phone numbers collected elsewhere cannot be used as a replacement for app tracking on iOS 14, regardless of whether they were collected with consent.
Developers will only be able to get permission to use identifiers for ad tracking on iOS 14 devices if they’re collected through Apple’s own AppTrackingTransparent framework.
Would Chrome institute a similar policy? The question is “would” rather than “could,” because Google could disallow hashing as an encryption method, but whether it would do so, with antitrust complaints flying in from every direction, is another matter altogether.
Perhaps the bigger challenge email-based industry initiatives face, at least in the near-term, is scale.
Although Criteo is busily working to develop a consumer-facing single sign-on user interface for publishers as part of UID 2.0, there’s just no easy way to get people who are accustomed to web browsing with no strings attached to suddenly start coughing up their email address.