Now that you mention it, in 343i's holding of the canon it's something that's lately shown. Halsey considers Spartans as humanity' next step, and humanity wants to mass-produce Spartans, possibly going through the same path as the Forerunner. The question now is, how humanity in the UNSC moves through it.

: - 9-year old SPARTANs forming the "software" in their minds that
: will govern who they are when they're adults, and the "parental"
: efforts to help shape that (fostering of adequate levels of compassion
: and/or other desirable qualities so that humanity is not simply creating
: obedient, heartless killing machines out of these genetically-endowed
: geniuses) from Halsey, Mendez, the trainers, the contracted
: specialists/experts, and the AI team responsible for the incredibly
: expensive S2 project.

I wonder if it would need a longer story for it, perhaps a series of three short stories, since it would be something of a character development arc. Not that it wouldn't be fertile territory for a tragic story.

One thing that would also be deliciously tragic is the story of a Spartan trainee going through the cycles of denial, indoctrination, forgetting his parents, coming to admire the UNSC, being devoted to his cause, being augmented -- and failing. And facing the existential crisis that his life was for naught, that his purpose to fight would never be fulfilled. Writing this in Serin's perspective would work really well.

: - Civilian perspectives on an invasion

I like reading and seeing about these in canon. It shows a perspective of utter terror. The first issue of Halo: Uprising is very powerful to me because of this. Imagine being a civilian that's only gotten to know little through ONI's propaganda how the war goes, and then seeing with absolute, helpless terror at what the war is really like. Thinking that the Covenant would even respect wartime articles.