To get things started, I would like to give two possible story lines that I could see happen:
1: After the Elder Scrolls were scattered all throughout Tamriel, the next game could be like Arena and take place all across Tamriel. The main quest could delve into what the Elder Scrolls actually are and what is their true purpose.
2: This one might be more probable, but it might take time to explain. First off, i want to say that I think it would be in Hammerfell. Not because I extremely like Hammerfell, but it seems to be the focal point of the next game. In Oblivion, I distinctly remember hearing many Nords say "I'm from Skyrim" and just an overall impression that was more profound than any other province besides Cyrodiil. Also, the Great War seems to be fought harshly in Hammerfell, what with the Thalmor taking territory there and some Alik'r warriors/Redguard woman in Whiterun saying the resistance to the Thalmor is "alive and well in Hammerfell".
The story behind this game in Hammerfell would be the return of the Dwemer. I have a theory behind this as well. There are Dwarven ruins in mainly 3 provinces, Morrowind, Skyrim, and, you guessed it, Hammerfell. This is where they chose to make their home, throwing Volendrung i believe(or some other hammer maybe) and moving to where it landed, thus naming that province "Hammerfell", literaly where the "Hammer Fell".
One last thing is that in the first part of the game, when you encounter Frostbite Spiders for the first time, Hadvar says "What next, giant snakes?" And I think they might do that n the Alik'r desert.
I do not think Hammerfell will be the next location, as they have a game set there already (though it was not very well received). I think they will try to cover all the places then redo them all together like as they did in Arena. As for the next one, I think it will be one of two places. First off Black Marsh as they did take time to develop the Argonians and setup some good backstory such as:
·The saxheel jewelers.
·Shadowscales, that would setup a Dark Brotherhood faction quest to establish them again.
·The Argonians being a formidable force to stand against the Thalmor .
The second one I think would be possible would be a combination of Valenwood and Elsweyr. This could function like the civil war with the Thalmor starting to fracture due to the Dragonborn strengthening the Empire (either by helping the Empire or Stormcloaks via the civil war quest). Having two countries to go back and forth would spark an interest (though it would not really be any different than any DLC where you go to a new land). It would still be a great feature that I am sure they would ride into the ground with marketing. They have already established a bit on those two places.
No matter what they decide though it will be a long wait as the next game will most likely be Fallout then another 3 years after that to get to the new Elder Scrolls. Though I still hold to my idea that they will cover each of the provinces, and then do a “Final” one that lets you experience all of them together.
I think it would be awesome if they added the bigger and badder lich king armor set. Also it would be awesome if you could travel beyond more than one providence in tamriel. It would be awesome if the lich king was part of the main quests either you chose to make friends with him of chose to fight against him with a group (some kind of guild). bringing back the dark brotherhood would be pretty cool also, if you chose the lich kings side at the end if you unlock the highest level of smithing and you compete that questline you get to craft the armor it would be cool like my profile picture. And there could be a new emperor of tamriel so you could choses his side or the lich kings. It would be cool to be a questline of the nords attaking elswr and you must help the khajiit and defeat the nords. I hope this showed you something.
Not to sound a bore, but while speculation can be fascinating, anything could really be included in TES VI, and new lore will likely be added to back it up. I doubt any of us could have predicted the events of Oblivion after Morrowind, for example, or the events of Skyrim. That said, I would quite like to see Hammerfell, and while I like the Summerset Isles, I would rather Bethesda waited for better technology give the province justice. A few points I would make are, however:
1) We already know what the Elder Scrolls are, and I suppose what their 'purpose' is, but I would say that no everything neccessarily requires a purpose, if not created for a specific reason.
2) Unless they chose two smaller provinces like Valenwood and Elsweyr (and even then, I think sticking to one province is best), it is unlikely that Bethesda will include multiple provinces, let along the entire the continent. There is no way we get the detail in each province that we are accustomed to. Even in TESO, the full areas of each province are not accessible, but rather only limited areas.
3) Why would the Nords attack Elsweyr? And I think choosing the Emperor's successor is a bit controversial. The Empire does seem to operate under primogeniture, and while we have seen in the past that sometimes 'Might makes Right', I see little point in plunging the Empire into chaos for such a petty issue (comparative to the other events going on).
I think it makes the most sense for the next game to be in Valenwood, Hammerfell, or Black Marsh. Although I'd love to Elsweyr, I don't think it'll in the next game. I find the Summurset Isles also unlikely because the next will definitely revolve around the Aldmeri Dominion and unless that game involves destroying the government from it's headquaters, I don't think it's likely.
Valenwood would be great because it'll be a great place where we can really see the Dominion in action, seeing their cruelty in new, more political ways. I find Hammerfell as likely as Valenwood, Hammerfell has had to fight off both the Dominion and secceed from the Empire. Hammerfell's storyline would likely involve yet again fighting off the Dominion. Black Marsh is also a good choice for the next game because of how isolated it is from the Empire and the Dominion during the even of Skyrim. Like Hammerfell, Black Marsh secceeded from the Empire and might have fight to fight off the Dominion. They'd also use the Black Marsh game to reveal more about what Black Marsh did to Morrowind.