QUESTION: if I run my own system with local accounts, full root access, and no remote accounts... why should I care about whether systemd "MAY BE ABLE" to store someone's date of birth?
Sounds to me like, for all I care, they could add fields for ethnicity, religion, d size, political orientation, colonic maps, or whatever else they want.
If it's to build systems shared with underage family members, schools, or other public system... I personally DGAF.