Comment 6 for bug 1861239

I just learned about Latanya Sweeney's research in a training. According to her paper, 83% of people in the United States can be uniquely identified with a combination of Zip code, date of birth, and gender: https://dataprivacylab.org/projects/identifiability/paper1.pdf -- we don't usually store gender in Evergreen, but it certainly suggests that we should be careful with the postal code and date of birth.

If we do use the opt-in approach, we really need to publicize it well!