I am applying to the MD/ScM program, and it is my understanding that they are interested in attracting people who want to be PCPs but others can apply too (
http://www.brown.edu/academics/medi...opulation-medicine/frequently-asked-questions):
Q. I'm interested in population medicine, but not in primary care. Can I still enroll in this program?
A. Yes. Although our goal is to graduate more primary care physicians, we understand that students' interests change over time. Health care will need physicians trained in population medicine in all specialty areas. Enrolling in this program will not put students at a disadvantage if they decide to apply to specialty fields other than primary care.
It also seems to be more pop med focused rather than policy, but worth looking into further.
I think that writing well about the type of practice you imagine for yourself says a lot about how well you understand the way medicine is practiced and where things are going in the field.