i like both of your ideas, and i did also notice the halo 5 in the clouds and sand. I honestly believe they are on the one forerunner planet that shoots down ships and is the only thing there. it was used back in the flood forrunner war to defend the forrunners from the flood and it can shoot down ships in slipspace. it had a fatal error during that time and now shoots all ships when they fly by, it happened to the covenant and human in the covenant and human war. so this is just what i think personally, but i could be wrong easily.
and one little thing and pointer, did any of you see pride rock in the back ground of the trailer?