Hi! I don't have any good advice for you because I am working on a very similar type of SOP, but I can tell you what a few professors have recommended to me. The feedback that I've been getting is to outline a general interest -- but one that is specific enough that you can say why a particular program interests you. That advice might not be very helpful since I'm looking into MA programs in anthropology. Essentially, everyone has assured me that not having a thesis topic outlined is totally fine (normal, even!), but what they do want to see is that you have a general direction and some concrete ideas you want to explore. I'm sorry I'm not someone who can speak from the experience of being accepted, just from a fellow sufferer!