Personalized medical advice is problematic in many ways, and I don't see how it would make a good SE site. SE sites work best if the questions and answers are useful to future visitors, a personalized diagnosis doesn't fit that idea. They are also impossible to do well, I'm not a medical professional, but from what I understand a remote diagnosis without examining a patient, with no access to previous medical history and a likely very incomplete description of the issue from the patient is irresponsible in many cases.
We can't prevent people from treating answers on the site as medical advice, the only way to do that would be to not create the site in the first place. But questions asking for personal medical advice simply are not good questions for an SE site, that is a sufficient reason to disallow them.
I fully expect that the site will have to establish a Skeptics-style citation requirement for all answers. Health topics tend to attract a lot of problematic answers on the internet, and this proposed SE site likely won't be an exception. Such a rule can help a lot with removing low-quality answers and increase quality at the expense of being rather hostile to new answerers.