If you think about it, the mantle of responsibility basically refers to a mastery of STEM (science, technology, electronics, and mathematics). Robotics and AI have become the locus of power in the Halo universe, and the old ways are fading. Cortana has always served that role for John, but now he's adrift.

I think Halo 6 will see John 117 set out on a new character arc where he retrains to be effective in this new world. They'll thaw out the MC, run through controller calibration, but this time they do it properly with a hypothesis, a well designed test, and a careful analysis. The campaign could branch to 4 perspectives:

John = SCIENCE
Locke = TECHNOLOGY
Thel 'Vadam = ELECTRONICS
Halsey = MATHEMATICS

They'll have to come together at the end and put it all together to prevail.

If 343 goes this route, the player can grow with the chief and learn what it takes to grapple with Cortana on her own terms. Good for STEM outreach and a healthier perspective on masculinity. Players can assume the mantle in their own life(!)

Thoughts?