There are many possibilities for Elder Scrolls 6's time setting, and one of them is the War of Thras waged against the malicious Slug People. If the series chooses to go back to the past, the First Era could be a great way to show off some of its more esoteric lore, and as a particularly impactful event in Tamriel's history, the War of Thras is a good candidate. The setting for TES 6 isn't even known yet, and with Bethesda focused on Starfield for the time being, it doesn't look like news will come any time soon, but that only leaves room for more possibilities.
The War of Thras was a response to the Thrassian Plague created by the Slug People - also known as Sload - of the coral kingdom of Thras. There's a lot of weird Elder Scrolls lore that TES 6 could cover, and this is one of the odder ones. The All Flags Navy, led by Bendu Olo, devastated the Sload people in a brutal massacre that the species never truly recovered from, before sinking into Coldharbour, the realm of Molag Bal. After, the Cyrodiilic Empire expanded its power in Valenwood and Elsweyr; the war, if it can be called that, helped the Empire become what it was during the events of games like Oblivion and Skyrim, so it was a highly important event in its history, and indeed that of all of Tamriel.
The Thrassian Plague and the resulting war are just one possibility among many for possible settings if the next Elder Scrolls returns to the series' past. There are others, like Tiber Septim's conquering of the continent of Skyrim, or the human uprising against the Ayleid. If it showed the future instead, TES 6 could have an anti-human apocalypse. Still, the nature of the All Flags Navy and the unique setting that the First Era could offer make it stand out from the rest, allowing players to pit their wits against the Sload and other creatures they may have rarely had the chance to encounter.
The Sload are the native residents of Thras, an archipelago located near the Summerset Isles in Tamriel. They are a large race of beastmen described as being akin to slugs. The species as a whole is apparently highly selfish and lacking in empathy, incapable of feeling emotions other than greed, and always looking out for their own self-interest. They are also grotesque, with a highly offensive odor. Sload Soap is an alchemical ingredient in TES 3: Morrowind, which is made by adult Sloads from immature ones. If the game does go back to the Thrassian war, then they'd likely be the villains of Elder Scrolls 6, since they were apparently one of the most hated races in all of Tamriel. Their frequent attacks on the Summerset Isles' Altmer, making use of sea monsters, "infernal machines", and the species' talent in necromancy, make them unlikely to be any form of ally.
The Thrassian Plague is a sickness originating from Thras, believed to be engineered by the Sload. It was devastating, wiping out half the population of Tamriel as well as a great amount of livestock, and was what led to the War of Thras and the Sload's near-extinction. It caused an unceasing thirst that made those afflicted with it drink to the point of vomiting and eventual death. According to Kindlord Nemfarion of ESO, "The afflicted drank themselves to corpulence with each passing day, until their bones cracked under their bulging flesh." It's just some of the Elder Scrolls' lore that hasn't appeared in games, and that might be a good thing. Such a fate sounds horrifying, and coupled with the Sload's already-awful reputation, it's not hard to see how it led so many different kingdoms to come together in the All Flags Navy to attack them.
If Bethesda did decide to make the War of Thras and conflict against the Sload a central point of TES6, there are a few ways it could be done. The war itself likely wouldn't be the main plot, and the game could start before the war, when the Thrassian Plague was still ravaging Tamriel, rather than closer to the resolution of the war (as Skyrim did). Players need to pick a side in Skyrim's civil war, but it's hard to imagine siding with the Sload, especially since their kingdom and population were devastated so badly afterward. If there were multiple factions within the war and the All Flags Navy, then that could help introduce some choice to the main quest line. Bethesda has some wiggle room with what it can do to give TES 6 the ten-year lifespan it's promised, especially since most of the details of the War of Thras are shrouded in mystery.
It may also be best for the story to extend past the war, and not transition directly into the post-game after it, as Skyrim did with Alduin's defeat. After the War of Thras, most of the All Flags Navy sank into Coldharbour, the domain of Oblivion ruled by Molag Bal. TES 6 doesn't need every god and daedra, but if this were indeed the course of the game's story, then Molag Bal's absence could be strange. This ending hardly seems satisfying, and doesn't really seem like it allows for much post-game content, so the end of the war wouldn't be the end of the game. An escape from Coldharbour could be a good final quest, though it would risk being too close to ESO's first main story arc. The War of the Uvichil would be a perfect candidate, as would the Empire's conquering of Valenwood and Elsweyr following the War of Thras. The game could require some well-placed time skips depending on how far across Tamriel's timeline it chooses to stretch, but that could be a benefit if Bethesda does it right.
Of course, if the next game did go back to the War of Thras, it could bring new features with it. TES 6 can explore new magic and exploration options in the mostly-aquatic world that an island archipelago and a fleet of ships would bring. Underwater combat and being able to steer a ship across the oceans of Tamriel are both exciting features that might come to Elder Scrolls 6 in a world with so much water, which would help the next game stand out from Skyrim. There are even more possibilities, like a focus on spear weapons or water magic. Almost anything could come to TES 6, especially in a unique setting like Thras and the nearby Iliac Bay.
Perhaps the most exciting possibility is a new playable race, and Elder Scrolls may already have the perfect one. TES 6 could introduce many playable races that haven't been available in past games, but the Maormer would perhaps be the most likely in a Thrassian setting. Also called Sea Elves or Fish Elves, they're a semi-aquatic race from Pyandonea, a continent near the Summerset Isles. Given that Thras is also nearby Summerset, this is quite possible. Maormer have already been NPCs in ESO, so taking them to a playable race in TES 6 seems like a logical step forward. They could add exciting new elements to the game, and their ability to breathe water could be of great help when navigating the waters of Summerset and Thras. Elder Scrolls 6 has countless possibilities, and while the War of Thras and the Maormer it could introduce are only two among many, it would be fantastic to see something wildly different from the Elder Scrolls games that have come before.
