I think it's going to be High Rock, personally.
Looking at map formations, sunset, etc. High Rock has the best opportunities (assuming the geography in the teaser is worth anything), the music makes me think more of Bretons, and I think the themes in High Rock might be particularly popular right now, especially with series such as Game of Thrones being so popular. High Rock is essentially like a magical medieval England/France, and I assume the geography could be quite interesting. With a High Rock setting there could also be some expansions on orcs, a look at the Hammerfell (dlcs involving Hammerfell and Orsinium, maybe? maybe there could be a island off of Hammerfell we can do to, similiar to the Solstheim dlc...), and we could see stuff relating to Skyrim, too - maybe Forsworn are being slowly pushed into Hammerfell because of events going on in Skyrim, and the PC has the opportunity to address it.
Hammerfell
could be interesting... Or it could be a lot of deserts and, well, kind of boring? I'd much rather see Bethesda continue to do more environments because after Fallout 3 and Fallout: New Vegas, I really,
really don't want to see more and more
sand. I'm practically set up on sand for the rest of my life, at this point.
I could probably deal with Elswyer if they made it interesting with say, buried pyramids, lush oasises, etc. with an expansion on the Khajiit - which I would LOVE to see in game, since we've only seen 1 khajiit morph at a time in game (besides ESO, I guess) - but... ehh. I'm good for now. I just don't really find Hammerfell to be too interesting, outside of the whole "Redguards are not native to this plane and they killed an entire group of elves" tidbit.
I'd prefer Valenwood as a setting but I think it's fair to say the teaser doesn't look anything like Valenwood has been described... so if it was Valenwood, I'd be really confused and surprised.