It's currently part of the conversation at W3C, advertisers aren't particularly happy about FLoC either, they'll need to build a lot of ML to correlate the FLoCs with their customer's campaigns, one by one, until they find the group that performs. They'll need to develop techniques for this, for example using machine learning and train their models. That's not how this stuff is typically bought today.

In particular they aren't happy also about the 3rd party cookie comparison because it just makes no sense, not sure why the PR focuses on that given that this is minimum 3-4 orders of magnitude less precise than 3rd party cookies, targeting a FLoC is going to be like targeting a zip code, hardly THAT privacy invasive.