Halo Infinite will be set on Halo Installation 07, where Master Chief will face down a faction of former-Covenant mercenaries known as the Banished. However, if the next game is going to focus its story on the battle with the Banished, it may need to jettison some of the other story-threads hanging over Installation 07.
If Halo Infinite tries to deal with all of the plotlines that could be addressed on Installation 07, the story will likely lose focus. Overall, as long as it pays off on major thread and delivers a solid experience, this could be okay for many fans.
Atriox
The Banished was founded by two Brutes named Atriox and Decimus, who led a group which split from the Covenant during the Human-Covenant War. For a time these mercenaries mostly engaged in acts of piracy against Covenant ships, but were later able to claim many of the Covenant's resources after the Great Schism at the end of the war.
In Halo Wars 2 the Banished came into conflict with the UNSC, and Decimus was killed. The Banished had been trying to capture the Forerunner Ark which controls the Halo Array. Halo Infinite's teasers have revealed that Atriox will no longer be leading the faction in the next game. Instead, the Banished will be led by War Chief Escharum, who appears to have taken over Halo Installation 07. Atriox's whereabouts and potential return is one of the major plot-threads overhanging Infinite.
The Flood
The arrival of the Banished is far from the only plotline hanging over Installation 07. In 2258, just a few years before Halo Infinite, the Elite faction known as the Swords of Sanghelios discovered and contained a Flood outbreak on Installation 07. They were later joined by the USNC, with both factions monitoring the Halo ring to make sure that there were no further Flood outbreaks.
It seems very possible that now that the Banished have taken over Installation 07, the Flood may be able to regain its strength without their knowledge. Installation 07 has a history with the Flood, having been taken over by the Flood Gravemind known as "the Primordial" during the Forerunner-Flood War. Like all of the original Halos, Installation 07 was designed partially to study the Flood, and, if necessary, to form the Halo Array and wipe out all sentient life within range to starve the Flood to death.
It wouldn't be the first time the Banished have encountered the Flood either. Shortly after the death of Decimus, the Banished would accidentally release the Flood still living in the remains of the High Charity, the Covenant's space station capital. Though they eventually overcame the Flood the Banished took many casualties.
The Story Of Halo Infinite
Halo Infinite doesn't need to deal with the Flood or Atriox's whereabouts. First and foremost it needs to focus on making War Chief Escharum a compelling and complicated villain. Much of the backstory for Installation 07 and the Banished comes from the Halo novels and Halo Wars 2, which many fans of the main franchise will not have followed. Infinite cannot rely on fans being invested in hanging plotlines from games beyond the main series.
Halo Infinite needs to tell a story which doesn't require knowing that lore, but is instead able to stand on its own merits. While certain elements like the Flood will likely return, this should be done in a way that remains relatively self-contained, and helps Halo Infinite's story flourish in its own right.
Halo Infinite is expected to release in Fall 2021 on PC, Xbox One, and Xbox Series.