One of the more sardonic takes after the last trailer was that the core concept of the game was going to be vehicle building, and that the game's logo is even supposed to be a tire, but I think the game play demonstration showing how extensively the "fuse" ability runs makes me think the overall theme of the game really has to do with combination and connection, both from a game play and narrative perspective. From a game play perspective we're building weaponry, tools and vehicles through combination, effectively forging new possibilities. The logo of the game is two dragons connecting into each other. Meanwhile a lot of the game carries imagery associated that serves as an antithesis to remedy; Zelda gets separated from Link, disparate Sky Islands and debris disconnected from the world, landmarks like Korok Forest being torn away from Hyrule, etc. The PR blurb also mentioned earlier last year that Link and Zelda's devotion to one another would be key in saving Hyrule or some such.
I'm very interested how the story is going to play out with this in mind. BOTW was a very meditative game which game play wise felt rooted in a similar sense of self-discovery, not just about Link's backstory but about the player's ability to decide their own path and way to play. TOTK naturally has the Zelda and Link connection as the backbone, and it has a lot of potential since Zelda herself was the most compelling character of the last game, but there's a lot more they can dig into the world of Hyrule itself. I feel like building Tarrey Town in BOTW was almost like a precursor to this theme, it felt like you helped make a small part of the world into a better place. By connecting all these people from different parts of the world.