Some ad networks are already taking in user data through hashed email addresses. There are other things that can be done though. Google Analytics supports User

Some ad networks are already taking in user data through hashed email addresses. There are other things that can be done though. Google Analytics supports User Id's, so you can do a better job at attributing to specific users across multiple devices. GA has traditionally discouraged passing this PII into it's platform but is now supporting this limited ID information. Other analytics packages have allowed this type of identification information for a lot longer. Specific to advertising, there are also other tactics you can use to value your impressions that don't involve individually identifying people.