I think this is interesting but it's also obvious the map is going to change. One of the most significant landmarks of the first game - Hyrule Castle - is ascending into the sky at the end of the trailer. It's a very obvious sign that while this is a world we've been to before, it's not going to be the world we know inside out - which is why that shot has us looking out from the Great Plateau. There are mysteries in the original game, like the Zonai Ruins and labyrinths, which remain unexplored - given the reveal trailer emphasises an underground space so much, I do wonder if that's going to be a feature of the map: substantial subterranean areas.
I don't think this is going to feel like DLC, but I do think it's going to be a much more direct sequel than we've ever had in Zelda before. It's going to pick up threads in a way a sequel like Majora's Mask simply didn't. That trailer hints we're going to get more of Link and Zelda's relationship - and likely more character development of Zelda as someone fascinated with the past and burdened by her duties. As I've suggested above, I think the Zelda team are going to take some of the mysteries they didn't explore in BotW and expand on them - especially the ancient civilizations. And, clearly, Ganondorf is likely a significant feature of this game. Calamity Ganon is seen as a force of nature and a primal, metaphysical being more than anything , and the history of the man he was has clearly been lost. The Gerudo have tales he may once have been of their tribe, and the Zora histories don't connect the "evil man with designs on ruling the world" with Calamity Ganon.
So the core relationship of the series - between Link, Zelda and Ganondorf - is only implicitly explored in Breath of the Wild, but could well be a key focus in this new game. being set in the same 'world' doesn't just mean the physical landscape we've explored - which I expect is going to significantly alter in some way - it means also being grounded in the narrative tropes and themes that BotW hinted at, but didn't fully explore. I'm not sure why this is a huge cause for concern - this game has been in development for around 18 months and has at least 16 months of development left, in all likelihood. On top of that, plenty of other art forms and mediums of entertainment aren't afraid to re-use locations and worlds and relationships by expanding on them in sequels.
EDIT: I'd also point out after E3 2016 that people were claiming Breath of the Wild would feature no towns and would be terrible as a result. We've seen one minute of footage (which I do think hints at some key ideas for this game, hence being used as the reveal) and has some cryptic statements from the developers. Let's not lose our heads.
