I have a suggestion to improve your idea: Allow the user to deny the FLoC if they wish, by redirecting them to a byzantine "Preferences" page with 2 dozen options to opt in or out of. Promise to apply the user's choices within 7 business days.
Bonus points if you make the preferences page a dungeon that users have to navigate with twisted meanings and options that work counter to the user's actual preferences.
Critical hit if the preferences page has toggles that actually don't toggle, and just remain "on". This tracking data sent to a third part is certainly crucial in development of a website.
And after going to the site, and being forced to toggle every opt-out option individually before saving... if you return to the site later none of your opt-outs are shown and you have to redo everything each time.
Well that was your fault. The seventh toggle on the list was clearly labeled, "Use cookies to track my choices for the preceding six preferences and the following eight preferences"