Even if the overworld was hypothetically 1:1 with BotW (quite doubtful tbh), there is still so much that they can do to keep it fresh.
- As others have said, I do believe we will also be going under ground if that teaser was any indication. (For all we know there could underwater segments too.) Imagine if this was a hypothetical Super Metroid to Metroid 1, a much more expansive world?
- Not to mention they may have the world looking far more lively since they will be going through a period where Ganon has been (temporarily) defeated. New shrines and bigger/more dungeons?
- The story will likely be taking a bigger role going by Nintendo's comments over it being even darker than Majora's Mask.