None, it should be something new and unique, something utterly alien. Unfortunately as most humans can only comfortably absorb what they already find familiar, something actually alien would be so incomprehensible as to drive us insane (or at least unsettle us greatly), which I imagine would be counterproductive to Bungie's business plan. Whatever it is it will probably be derivative and more than likely some kind of reskin because that's honestly what I've come to expect.