Looking back, Halo 2’s split campaign was a fresh, bold move; offering another perspective of the Covenant War, thus a richer story, and great, new gameplay possibilities (Working with Elites :D).
So… how bout reintroduce the split campaign in Halo 5, with the Didact instead to give new perspective for the Forunners!
Story: The Didact’s campaign could take place 100,000 yrs. ago with the Forunner Empire and the Flood wars; adding a new level of back story and depth. For those who read Greg Baer’s Forunner trilogy, the campaign could easily use that as a starting off point; imagine battling Flood again, Advanced Humans, and even Precursors. Most importantly, Mendicant Bias would be introduced; allowing for His total backstory to coincide with Master Chief discovering him in the present campaign. Mendicant Bias has been hinted ever since H3, and this would establish his character without confusion or unnecessary mystery.
Gameplay: Halo 4 really displayed the power of Didact to a great degree: Telekinesis, command over Promethians, levitation, etc. Now imagine a Didact in his prime; new Forunner weapons, crazy melee attacks, and oh the War Sphinxes! Didact’s powers and strength would be immensely great, but necessary for an immense challenge.
End Result: Didact’s campaign would be long and tragic, but would lay the foundation for Master Chief’s present day adventure. Seeing from the trailer, Master Chief seems to be going on an odyssey throughout the galaxy, and what not better for Didact’s campaign to interweave location by location, separated only by time. The end of Halo 5 could reveal Didact’s still alive, now confronting Chief face to face; with what the player has just played creating a sense of sympathy for both Didact and Chief. Just as Halo 1 set up the story and H2 expanded on it, Halo 5 can truly immerse the player in the Forunner story. So… would that be a good idea or no?