Also link to that source code mentioned: https://source.chromium.org/chromium/chromium/src/+/master:c...
Why would anyone care about that, as opposed to, you know, reducing the amount of tracking?
(Disclosure: I work on ads at Google, speaking only for myself)
When one of those cohorts is narrow enough to reveal something specific and highly private (like a specific disease / medical / legal / societally high interest issue) - what then? Sites get to learn that you are associated with that very private concern.
No. I am against any and every form of personalized AND aggregated categorization, because until the associations created are no longer used as criteria by others, no form of tracking is neutral.
Cookies AND FLoC and any other replacement all need to stop.
And those who want to characterize others need to stop, because the information WILL be abused.
Additionally, combined with just IP address its probably a 99+% precise user identifier.
How so? A user's cohort is shared by many other users, and for any individual site you have visited it is very likely there will be another user with an identical cohort who has not visited that site. This means you cannot tell exactly which sites any individual has visited.
> combined with just IP address its probably a 99+% precise user identifier.
IP address alone is already a massive fingerprinting leak, and needs to be addressed if browsers are to prevent cross-site tracking. Chrome is also working on this: https://github.com/bslassey/ip-blindness