Just a theory.
I’d like to think Halo 5:Guardians is just Halo 5. But given the prominent featuring of the ONI Spartan, the fact that this is the first numbered sequel to have a subtitle, and this promise of a ‘journey’ and wanting to push the franchise in new directions (and an ever present desire to compete with those dreaded yearly franchises)what if Halo 5 is two complete, but separate games, one from The Oni’s perspective and the second from The Chief’s perspective, both on opposite ends of the same events, coming out a year apart? That might explain the box art. The sequel box art would have Chief on top.
Just speculating. Fun to imagine. It’s probably not going to be anything we imagine. I doubt it will be like Halo 2 where it switches perspectives throughout. I think that’s a little too predictable (as cool as it would be) and they know we’d think that and are about to pull the rug out with something bigger.