Yeah ok this sounds crazy but what if the campaign was split three ways? ‘Dean you’re crazy! Halo has never had a three viewpoint campaign before, that would be madness’ you say? Well listen up cause I’ve been doing some thinking about this.
Ok so from my own extensive knowledge of canon here is a theory. My guess is that we will play as Master Chief, The mysterious new spartan and a forerunner. The current time campaign will feature MC’s rouge adventures from the Ark to Sanghelios in search of Dr. Halsey and Mendicant Bias in an effort to resurrect the ‘dead’ Cortana. On the other side of the scale is the mystery spartan. Lets call him spartan X for now. X is a spartan VI trained specifically for Lone Wolf assassinations similar to Noble 6. His mission is to hunt down and assassinate the Master Chief who is suspected to have gone rouge and join Halsey and Jul M’dama. So the cycle will be like Halo 2, with 1-2 missions from the chiefs viewpoint, then to spartan X’s with a time gap between them. The game will climax with Spartan X confronting Chief.
But every 2-3 missions in will be a flashback playing as a new forerunner character . It will follow the end of the forerunner-human war and the entire forerunner-flood war. This way we can reveal Mendicant’s betrayal of his race AND use the Flood as a plot point without breaking canon. Ancient Humans can be enemies for the first half of this subplot, while the flood for the second half. Throughout this subplot we can fight along side the Didact and his Promethean’s. The subplot will be set mainly on a forerunner planet (ie Halo legends: origins) and a little on requiem. At the climax of this subplot, Mendicant Bias’ betrayal ultimately results in the death of the forerunner protagonist, think Reach’s ending but with flood.
That’s the basic skeleton of my theory, so please feel free to judge it, add in your own thoughts or whatever.