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.
