That's an Elder Scrolls theme, not exclusive to Skyrim AFAIK.

All of it

thanks for clarification ;)  But it has norse lyrics, if it is not only in skyrim why norse lyrics?

it'd be nice if it was set in the Black Marsh.

Bear in mind that we saw a glimpse of land in the title reveal trailer. We do not know for sure that it will stay true to that glimpse of land 6 more years from now.

1) Leaving Tamriel looks unlikely, at least to me.
2) I think vvardenfell, cyrodil, and Skyrim are out of the equation, we are not revisiting those places.
3) The map has to be bigger than Skyrim, since the game will two generations later.
4) Based on this I expect a combination of Elsweyr, Valenwood and Summerset all together (maybe even black marsh.

It immediately screamed High Rock to me... even seemed like that ruined castle atop the hill could be the ruined Orsimer capital (though that latter part is certainly a stretch).

Everything about that region says High Rock, and given its connection with Hammerfell I wouldn't be surprised if it involves both. If not, people should remember that just because it's a smaller province than Skyrim the devs don't need to make a smaller game world... they can scale it however they like. It seems odd to me that people seem to believe it needs to be scaled exactly to the same ratio that we saw in Skyrim given they've modified it in every single game. 

Between the western medieval setting, the drama surrounding the bretons, the conflict with the Orsimer, the decentralized chaos of the region, and the (probable) presence of the occupying Aldmeri dominion, it is easily the best province for the next game in my mind.

I think that trailer was hastily put together, just to put a logo someone somewhere, and has no indication on where the game will be set. Also, ESO is set 1000 years before the main timeline, and a lot can change in that time.

Assuming they are staying true to this layout, wouldn't high rock alone be way too small? And yes, high rock+hammerfell is likely too, now that I look at the combined size.

You're assuming they scale to the same ratio that they used in Skyrim, which was obviously drastically scaled down from what it is meant to actually be. They can make High Rock a dozen times larger than what we saw in Skyrim if they so choose... they've changed the scale with each new game. If picking one province meant never picking a smaller one we would have had to end the franchise with Oblivion.

All the "modern" ES games (Morrowind, Oblivion, Skyrim) use the same scale, and are proportionate to each other. Since 2001 they have stayed true to this layout (even in ESO afaik).

They havent changed scale since 2001, so I doubt they do it here.

Game is still years from launch. maybe even devs are not sure yet.