The most likely location of the next elder scrolls in my opinion (my three favorite candidates are 1. Black Marsh 2. Summerset Isles 3. Hammerfell, would be overjoyed if any of these turned out to be the next setting)
Being the only province that have successfully fended off the Thalmor solo, we heard a lot about Hammerfell in Skyrim. Lots of racism going on, country in shreds after the war with the dominion that concluded with the second treaty of Stros Mkai, strong internal conflict between the forebears and the crowns bearing many similarities with Skyrims civil conflicts. Very different geographically from Skyrim (its considered the hottest province of Tamriel with large vast deserts). Great deal of fan hype. Currently houses the largest parts of Orsinium which would open up a whole interesting side story that we haven't had the chance to experience yet, the Orcs and Redgaurd being one of tamriels proudest and most honor bound races would create a very interesting conflict, my mind would be blown if you could partake in creating the first real province for the Orcs(finally!). The nibba memes would be amazing, also one of the largest provinces.
The seat of the Aldmeri Dominion, could wrap up the Dominions storyline. Maybe the most technologically advanced of the provinces, believed to be the most beautiful in all of Tamriel. Lots of magic integrated in ordinary lives which would be a large contrast to Cyrodiil and Skyrim. It would be more dictatorial than any previous Elder Scrolls game which may speak against it being a likely candidate but it would be a different path for the series where your freedom was constantly being threatened and freedom being such a huge concept in these games could create something truly interesting. A lot of racism in the Isles (Altmer fascists) which is one of the Elder Scrolls series main themes. We haven't seen a lot of Summerset Isles, could be a graphic smorgasbord, lots of fan hype. The smallest province in Tamriel, Bethesda could focus more on cool content than just focusing on making it larger which has been a problem with the previous games sometimes.
Only province in the games (except arena) which we've seen nothing of, a great deal of mystery involved. Handles trade and politics far different from what we are used to in the series. A lot of furry fandom are hyping the shit out of Elsweyr and it would probably garner Bethesda a whole new market and cause a furry outbreak. Different from the previous provinces geographically. Has a lot of Thalmor influence being part of the Aldmeri Dominion but wouldn't bee as dictatorial as Summerset Isles would, hence contain the freedom part of the series without taking to many risks. The Khajiit have told us repeatedly in Skyrim to come to Elsweyr. Elsweyr is although not as important to the dominion as Valenwood and Summerset Isles (worth mentioning), also one of the smaller provinces.
Widely considered the most inhospitable of all the provinces. We haven't seen much of it at all in previous games and it could be a believable hardcore experience if Bethesda choose to go that way although unlikely. Got a very interesting conflict going on with Morrowind, being able to finally strike back after Morrwinds constant slave raids and oppression after succeeding from the Empire (after the end of the oblivion crisis) Argonias people is now in a position of independence like they never have been. The Hist could be done extremely iconic if done well, has the coolest creatures and monsters in Tamriel in my opinion, could be downright frightening exploring treacherous swamps not knowing what could lurk under the murky surface. Also, right in the middle of the provinces concerning size.
What speaks against it is that it not belongs to either the Dominion or the empire, but maybe it could feature a storyline in which both the Empire and the Dominion are trying to claim it. Not many races other than the Argonians live in black marsh due to diseases, the large hostile wilderness and lack of conventional means of travelling, so that may be a concern for the believability of having multiple races there. This is maybe my favorite choice for the next elder scrolls because there are just so many cool concepts to be explored and there is a lot of fan hype for this one, could revolution graphics if done right.
Being a part of the aldmeri dominion, if the story was to take place in Valenwood the overthrow of the dominion would likely weaken the dominion so much that it would be no way to go but defeat for the Thalmor cucks. It has interesting architecture with its cities built on many levels high up in the trees (would be very hard to make so that it would be logical and so you wouldn't get lost all the time). It has the Wild Hunt which could be an interesting side story or backdrop for the main plot, the Wild Hunts incredible violence could prove a great contrast to the serenity of Valenwood, one of the smaller provinces (but the vast level-structure of the province make up for it).
What speaks against it is that not much has been heard from it in previous games and there is very little hype for this province, not much interesting is going on there at the moment and it would be a designing nightmare to make the level design work. It is also under the strict fascist rule of the Thalmor which poses the same problem or opportunities as Summerset Isles.
The only of the three provinces belonging to the empire that we haven't visited in the single player games since Daggerfall. Considering that the empire always has been a part of these games, would be a safe but boring choice considering its many similarities with Skyrim geographically (the mountain parts) The Reach in Skyrim is said to be quite similar to many parts of High Rock.
What speaks against it is that it is very similar to the two previous provinces in the Elder scrolls games economically and politically, there wouldn't be that much new and interesting to take the elder scrolls in a different direction, also we haven't heard any interesting from High Rock in ages. I consider the Bretons a boring race (along with many others), virtually no fan hype for this province, one of the smaller ones also (second smallest after Summerset Isles I believe).
Unlikely (for obvious reasons mostly)
We have seen much of Morrowind in the past games and the only thing that speaks for it is the state of affairs the province is in. Once a proud civilization Morrowind has undergone a large change due to Red Mountain erupting in The Red Year which was one of the most tragic events in the lore for me personally (genius move by Bethesda to remove the place that an entire game and so many good memories resided, I was brought to tears when I learned that the lava of red mountain had engulfed Vvardenfell and that it was no more). Due to the destruction of Vvardenfell and making large parts of the coast around it unbearable to live in due to harsh ash storms Morrowind was in a weakened state which prompted the Argonians to invade it as an act of vengeance for the pain and loss Morrowind had inflicted on them over the years. House Redoran (my favorite house, honor truth and bravery above all!) proved the factor that saved Morrowind from the Argonians and such became the major house of Morrowind.
While i would be interested to explore the new Morrowind (and the mainland of course) it wouldn't be an interesting way for the series to go.
The only thing that speaks for Cyrodiil is the fact that is the empires seat in Tamriel that it has changed from the days of the Oblivion Crisis in 3E 433 some 200 years ago, the sacking of the Imperial City etc. Also seeing the effect of the Dark Brotherhood final quest would be interesting especially in Cyrodiil (but its consequences will be seen in whatever province the next game takes place in. Again this wouldn't be an original way to go so just no... (I do regret the decision to include the main providence so early in the series, it should have been saved for last being the one with most epic history, lore and significant places).