I don't think it's unrealistic to assume that VI will focus on the High Elves and the plot will revolve around the Thalmor (maybe trying to gain control of the Numidium- again!). They teased it so much in Skyrim and never actually gave that plot thread a proper close. For this reason I think it will take place in Sommerset Isles (but really any other province could work). Akavir is too much work for Bethesda, since they'd need to actually flush it out with lore and whatnot. It would be cool if they gave us the choice of working with or working against the Thalmor, but knowing Bethesda the main quest will probably be extremely linear with very little option for deviation. In C0DA, iirc the Thalmor were partially responsible for the events that ended life on Nirn, forcing the inhabitants to move to Mundus. I recall Kirkbride saying that the Aldmeri Dominion is a major player in the end of times and in one interview he says they are actually successful in their goals. Whether or not they go with this now is up for debate.
It's not uncommon for Bethesda to foreshadow their next game either blantantly or subtely. Oblivion was foreshadowed heavily in Morrowind.
And Skyrim was foreshadowed in Oblivion: