Bethesda has heavily hinted that the upcoming Elder Scrolls VI will take place in Hammerfell. This is a pretty solid choice for a location since the deserts of Hammerfell make a great contrast from Skyrim's cold and icy landscape. Hammerfell has yet to be explored in any Elder Scrolls, so this should be a fairly unique environment compared to what fans have already seen from the series.
That being said, there are many amazing locations in the world of Tamriel and beyond that would be great to explore. Not only are some of the other regions in Tamriel worth exploring, but there are also some other lands even further beyond Tamriel that only exist within the lore as of now. These five locations would be amazing for an Elder Scrolls game to explore, letting players dive deep into some of the coolest settings that the series has to offer.
Black Marsh
A fan-favorite setting, Black Marsh is the swamp-like home of the Argonians that can only be navigated through its series of waterways. The Elder Scrolls Online players have already seen a small section of Black Marsh that have joined the Ebonheart Pact. This small taste of what Black Marsh has to offer shows a land much more habitable than what's been described up until this point due to a lack of toxic air that many once thought to plague the area.
There's also a lot that players don't know about Black Marsh, such as who or what is in power. There's also the Naga and Lilmothiit, two mysterious humanoid races that have not been seen for some time. The mysteries and unique features of Black Marsh would make a great Elder Scrolls game, giving Bethesda a chance to put the spotlight on the history and culture of the Argonians.
Akavir
Akavir isn't one of the many regions that make up Tamriel, as it's actually a separate landmass that lies to the east of Tamriel. This land is possibly one of the most mysterious locations that exist in Elder Scrolls lore, yet most players have probably come across something connected to Akavir before. The Blades, who played a significant role in The Elder Scrolls V: Skyrim, actually originate from Akavir.
Akavir would make an amazing location for an Elder Scrolls game due to the huge variety of races that originate from there. Monkey humanoids, primal demons, vampiric snake-people and goblins all call Akavir home. Given how important Akavir has been to The Elder Scrolls series, it only seems like a matter of time before Bethesda features it in a game. There is something to be said for keeping Akavir a mystery too.
Aldmeris
Aldmeris is the homeland of all elves, but there's no official confirmation that Aldmeris actually exists, with the elven homeworld only being hinted at in-universe through rough translations of text found in the Crystal Tower at the Isle of Summerset. What's known about Aldmeris is fairly vague, though the sense of mystery gives it a similar appeal to Akavir.
According to in-game lore, Aldmeris is built from infinite cities constructed from towers that stretch far into the heavens. The description is somewhat similar to a real-world metropolis, especially where it's said that no nature remains in Aldermis cities. The Altmer, or high-elves, are said to have saved the elven people from unknown destruction that may have been brought on by the gods.
Pyandonea
There's a bit more known in-universe about Pyandonea than Akavir or Aldmeris, but there are still plenty of mysteries that players would be able to explore. A rare elf variant called the Maormer, or sea-elves, keep to themselves, having been one of the few races to have not moved in droves to Tamriel. That isn't to say the Maormer weren't concerned with expanding their territory as they attempted several invasions of Summerset Isle.
Pyandonea itself is a tropical environment made up of several islands. All known lore about Pyandonea only goes up to the Third Era, which is around the time that The Elder Scrolls IV: Oblivion takes place. Past the Third Era, there aren't any documented accounts about Pyandonea or even the Maormer who lived there. After many, many years, a return to this tropical paradise would make a great plot for an Elder Scrolls game.
Elsweyr
Home to the Khajiit, Elsweyr is a region of Tamriel that's been featured in The Elder Scrolls Online. Players have been able to explore a portion of Elsweyr for quite some time, though the entire provenance hasn't been featured in an Elder Scrolls game since Elder Scrolls: Arena. While most of the settings on this list have a strong sense of mystery that would drive their hypothetical plots, there's a conflict in Elsweyr that feels like it's been designed for an eventual game that features the region.
Elsweyr is made up of two nations that are both ruled over by the Aldmeri Dominion, the Thalmor union at the center of Skyrim's Civil War questline. Depending on what Bethesda decides the canon ending to Skyrim's Civil War is, Elsweyr may be primed to have their own power struggle. If the Imperials defeated the Stormcloaks in Skyrim, the Thalmor's power would be severely weakened, which could lead to the Aldmeri Dominion dissolving and leaving Elsweyr to have an internal battle for power.