IMHO an opt-out system is never going to work for this

IMHO an opt-out system is never going to work for this. Story time: while I still worked at Facebook, there was a company wide project for data attribution to comply with opting out of personalization (I believe to comply with an EU directive but don't quote me on that). The idea was to identify the source of any data by esentially tagging it on a granular level. This affected all the offline data procesing and ML processes but also code (online and offline) where various tools and systems were being built to analyze sites of data usage to detect use of personalized data and respect opt outs where applicable. I made two predictions at the early stages of this: 1. The tools and systems would tell us "all data is used for everything" and 2. Creating new non-personalized data pipelines and add things to them would be far easier and faster than trying to remove personalzied data from existing pieplines. Then, things like ad performance become an optimizatino problem with a clear benchmark (eg new unpersonalized ad serving pipeline vs the old personalized pipeline). …