Well, the Wind Waker is obvious. I mean, they actually PLANNED for the game to have two more dungeons, and it's glaringly obvious where at least one of them would have been (Greatfish Isle). Add the various unused passages in Hyrule Castle (like doors you can't access on the outside), and how little of Hyrule you actually got to see beneath the waves... and well, there's a lot of room to add new content there.
Ocarina of Time could have been expanded too. Just adding a full ice dungeon that unfreezes Zora's Domain would have helped.
And oddly, Breath of the Wild too. You can actually see all manner of islands and landmasses you can't reach beyond the edge of the world, so adding in a way to get there would add a decent amount more stuff to the game's world.
Ocarina of Time could have been expanded too. Just adding a full ice dungeon that unfreezes Zora's Domain would have helped.
And oddly, Breath of the Wild too. You can actually see all manner of islands and landmasses you can't reach beyond the edge of the world, so adding in a way to get there would add a decent amount more stuff to the game's world.
