No matter who's in charge, a vast sea of Halo fans legitimately care about the series's fiction. Bungie and others have spent a decade crafting a pretty fantastic story through the games, comics, books, anime, and more, and despite a satisfactory ending to Halo 3, the Chief has plenty of other places to (potentially) go. Such as….
Return to Onyx
One of the most popular (and probable) guesses so far is that the planet-sized structure we glimpsed at the end of the recent Halo 4 trailer is actually Onyx. The "shield world" featured heavily in Eric Nylund's official 2006 novel The Ghosts of Onyx, and it's where the few remaining Spartan 2s and 3s – including fan-favorites Kelly and Fred — will be found. Dr. Halsey, creator of the Spartan 2 project and the basis of Cortana, made her first in-game appearance in Halo: Reach and was also last seen on Onyx.
The only problem is that Onyx was sort of destroyed at the end of the book. The entire planet turned out to be made of millions of Forerunner sentinels (the same flying bastards seen throughout the games), who disengaged from one another and decimated a Covenant fleet toward the novel's conclusion. Halsey and the rest of the Spartans found themselves trapped in a Dyson sphere — an inverted planet in a slipspace dimension adjacent to ours, naturally — and searching for a way out.
The Chief would no doubt be thrilled to reunite with his oldest friends, and Ghosts of Onyx left plenty of unanswered questions. If Halo 4 has even a slight chance of answer them, Microsoft's going to get even more of my money. I can think of a couple other options, though….
Marathon: Still going?
Halo 3's ending was hardly ambiguous, but one aspect left some questions dangling in our minds: A brief teaser clip unlocked after beating the game on Legendary showed Cortana and the sleeping Chief's busted-ass ship approaching a planet that looked quite familiar to long-time Bungie fans.
Halo wasn't Bungie's first franchise — as many of you probably know, back in the '90s the enterprising developers made a series of Mac games called Marathon. Thematically they were pretty similar to Halo; the Marathon games teemed with lone super soldiers, rampant AIs, and millennia-old structures. And the planet that makes its cameo in Halo 3's secret ending has a pretty big Marathon symbol on it. The inclusion of this otherwise pointless scene fueled the already-widespread speculation that the Master Chief and the protagonist of the Marathon series were one and the same.
Now for something completely different
Of course, it could always be about something else entirely. Although it seems new series stewards 343 Studios would be missing out on some incredible narrative opportunities if that's the case, the team probably has loads of perfectly decent ideas that have nothing to do with "the story so far." Say goodbye to the other Spartans, screw Dr. Halsey's mom complex, and forget the forerunners ever existed, maybe.
I'm sure other people have plenty of good ideas, too, so lemme have 'em. What have I forgotten?