My idea of how the 10 year plan will work is like this:
There are seasons and Years, like how Destiny is: seasons are minor content updates and events which add a few challenges and items, with a bit of story. Years are massive updates that add a ODST sized amount of content and story, where it’s just a expansion.
Then there’s this idea where every few years, instead of a new Halo FPS that is separate (physically and digitally), we get a DLC that is essentially a full game and sequel to Infinite’s story. Think how MCC operates.
The way I’d release it is we get a content rich launch, with the only timed events being Christmas and Halo 20th Anniversary related. Then in early 2021, we start getting Seasons and Annual expansions that focus on the aftermath of the game’s campaign. most, not all, of these updates/expansions’ lore tie together to lead to the sequel a few years later (though it’s structure so the seasons and expansions aren’t requirements to understand the story of the sequel).
As to what these updates would have, the possibilities are pretty vast. Maybe one season is focused on Osiris, and another is focused on a Banished Skirmisher shipmistress, with a few new missions, items, and locations added.
A Annual expansion comes and brings in the some Swords of Shanghelios (with Tul Juran, Stolt, etc. being possible main players) against Let Volir, or Alpha Nine going against Colony, all with a reasonably short campaign and a massive content drop compared to the seasons.
Then comes Halo Infinite Part 2, which could be about Atriox coming in to quash the UNSC or the Created being introduced, with a full campaign and new locations that may take us outside of Zeta Halo (though not taking focus away from it).
So those are my ideas on how the platform will go, what would yours be. Just to be clear, I’m not saying it will have RPG elements like Destiny where there’s power levels, just using their content drops as a example