TESOL vs. TES SP is the wrong discussion.
Meet TES V Online:
The game will take place on whatever other province they will decide on, most probably Skyrim as that's the one that's been trademark-registered by ZeniMax.
Some supposedly epic and massive shit -just like the Daedra invasion
- will be going on, most probably due to the recent events in Oblivion, and whatever it is, you won't be able to leave the province because of it. There you have your single player TES game, typical of last two games in the series.
Once you finish the main quest, you will be able to leave the province, thus join the online network -for a monthly fee of course.
Because Beth is stupid, they will realize only too late that having to finish the original game first to be able to join the network was a bad decision; but because they will have designed the original game to be a heavily single player experience, with lots of scripted events and hand-holding, they will most likely stick to it. However, they may offer a "stoy lite" mode playable online, where many of the "finer details" will have been axed.
After that, you will most likely be able to visit one or two more other provinces though, and again, most probably not the whole of them at once. As the "online main quest" progresses, you will be able to go to other areas of the present provinces.
Expect all kinds of micro-economics, like the official plug-ins for Oblivion.
Expect the first expansion 6 to 12 months following the release of the original game. You will now have one more province as per the "story", which will open up zone by zone within the province on a global time and individual quest-solving basis.
This 6 to 12 months until the first expansion will serve as an unofficial play-testing phase to smooth out the problems. Bethesda may pump out lots of free content to compensate for the lame tech-support they will unmistakably have and the unstable online component. I'd wager that the online components will even corrupt the offline game data (like game saves and characters) for some players.
With each expansion/province, desiring players will be able to continue the game offline, but their online and offline characters will be separate past the original game. Additionally, online game will offer a lot more of the same stupid quests.
A faint modding support will persist for those who want to mod the offline game.
Expect official contests to "push the story forward". Some story bits will be given, and works of modders who can come up with the best material, will make it into the official game, in the name of "innovative dynamic and always changing world of TES online lets players shape the world to their liking". Modders will be made to do the work of developers once more, and this time, only officially. Bethslaves.
Also expect guilds to play a insignificantly large role. Expect guild-master players who probably won't serve any purpose other than Xbox Live points (or whatever they are called).
Summer and her minions will be given the power to obliterate misbehaving players online.
I'd say that they will make the game a cross-platform, where PC, X360 and PS3 players will be able to play together, but Beth is severely lacking the technical expertise to even make their SP games work right, *BUT*, that's where $300.000.000 is coming in.
Now thinking again, the online portion of the game might be a X360 and PS3 exclusive, with only an offline version for PC players. They might show mercy and enable custom network worlds for PC players though, but that would mean an unnecessary allocation of the $300 million, and is way over Beth to realize as developers, being incompetent developers themselves. However, a year or two past the release date, some tech-sawy modders may discover some implemented but non-executed leftover network code, due to the game being a port from X360.
Years later, after several expansions, probably one for each province, the final expansion may see the rediscovery of the Akavir Islands off Tamriel and a whole new threat of epic proportions from there. Then the game will last a couple more years, before the next game which will "carry The Elder Scrolls saga to whole new leves" will come.
Morrowind and Cyrodiil will probably never be covered by any of the expansions/provinces, and these two provinces will always be off-limits.
Mark this post.
edit: Hmm, another option would be to put a few thousands of years between the SP game and the online game.