Anyhoo, I do have a few themes and suggestions:

- There's plenty out there that's been left to wither away without being explained or expanded upon. I always think fans have a pretty cool imagination when it comes to filling in the blanks for plot holes and teased things.

- Watching the History of the Covenant deleted scene from Halo 2 made me yearn for more traditional or culturally representative art in the universe. We hear a lot about the art of all these civilizations in the novels, but we've yet to really get a prolonged glimpse of it in a visual medium. Fan interpretations of their culture in paintings, calligraphy, sculptures, nature, and other forms would be cool to see.

- Along with traditional narratives, maybe you could have a specific writing submission for forms like poetry, encyclopedic entries, or things like the chat logs and documents we see scattered throughout the novels.

- Splitting up the overarching factions from a species or culture might make coming up with ideas easier. Instead of just having "Human week", you could have a theme that solely involves the UEG, UNSC, Insurrectionists, prehistoric Humans, or civilian life. You could also do similar things for the Covenant, on both an organizational level and for each member species.