AdjutantReflex

Well since the Forerunner saga is being released, that would be a good place to start for Halo 4. I mean think about it. Humanity finds out about the species who's technology was more advanced than the forerunners, their secrets long hidden deep within the confines of space. Now we have an enemy and a great idea for a story line to go with. Unless 343 has something else in mind, i would say that this is the highest possible story idea for Halo 4-6.