I don't think it could ever actually work in practice :/

Exactly. I can think of so many bad outcomes. Just the medical point:

both medically ("your sample indicates you may have a higher risk of dementia")

You know how this will end in the modern tech dystopia. In countries where health care insurance is not mandatory or there is a large gap between collectivized and private insurance, DNA would be used to reject or raise the prices for people with 'unlucky DNA'.

A government that could be trusted now is not necessarily trustable in the future. I am pretty sure the orange guy clan would love to lone their pockets by selling such information.

Also, apart from these issues, a lot of people simply do not want to know these things. Suppose that the outcome is "you have a 30% risk of dementia by 60". For most people such kind of information is hard to act on, while it increases worry significantly. I do think it can help for some treatable illnesses, enabling early monitoring.