Don't hold your breath: it's a big question, one that presumably even the professional/academic community can't all agree on, and we can't really expect to do better than them.
Science Fiction & Fantasy has long given up on the idea of even trying to define exact boundaries of "science fiction" or "fantasy", and their
policy on scope includes the line "If you're not sure it's SF but you think a good case can be made for it, it's on-topic."