What i mean is if Tes online is covering all of Tamriel, and Bethesda sets tes 6 in one of the provinces in the Next game we would have already explored most of the province in Online. It would not feel as good as exploring a province that hasn't been fully seen before.
So they should go somewhere else like Akavir with Tes 6. Just my opinion.

TES1: Arena covered all of Tamriel too, does that mean Daggerfall, Morrowind, Oblivion and Skyrim were pointless? Not to mention that ESO is set 1000 years before Skyrim, a lot of stuff can change over 1000 years.

First, many people who play the single player games will not be playing ESO.
Second, Bethesda has presented provinces more than once and probably will do so again.
Third, the games are more than just provinces. They are stories as well.
Fourth, I will play an Elder Scrolls game no matter where it is set. I'm sure many others feel the same way.

Precisely. As it is, a lot of people want to go back to Morrowind to see how it's changed in the 4th Era, and it's only been 200 years since we were last there (granted there was a meteor strike and volcano eruption, but still). Todd Howard mentioned he'd like to revisit High Rock, because he didn't feel it was done justice in Daggerfall.