Zelda has always had open world version. It is jsut hardware limitations they had so they appear smaller to a modern version.

Unlikely tbh, I think Zelda maybe turned into an answer for those who like games like GTA as even though the are other open world first party games like XC non of them are sandboxes like BOTW. Why I say GTA is that the are a lot of people who just buy the games to play around in them some not even bothering with the main story and BOTW brings a template that now offers that and allows the franchise to incorporate new staples like DLC now.

BOTW much like LOZ and ALTTP is now the new template and structure for the series, the's no going back for mainline games now.

Honestly, I'm in love with the art style, open world, game mechanics, and visuals of BoTW. This is the first time Nintendo has ever made a 3-d zelda game in which I hoped they would make a direct sequel to it building off the same engine. That way it would take a lot less time to develop a sequel.

Perhaps we could see Nintendo set up a three team development scheme:
One for Traditional 3D
One for the 2D style games
And one Large team for this new style.

I'd like that too. 
Why chose between 1 or 2 and not have all 3 of them?
Plus, they could structure it so that once the top down 2D game and classic styled 3D game are done, both teams can jump straight to helping the Open World team with finishing the game.

They'd have to hire a lot of people, Breath of the Wild had the largest development staff in Nintendo history as is. But, it would give us a steadier and more frequent flow of Zelda games to go around.

I genuinely don't know where they can even go from here. Why even bother for a long time? I honestly wouldn't mind a decade without another new 3D Zelda after this masterpiece, outside of a low-key Majora's mask sequel to round out that trilogy.

4 million units sold is disappointing?

Because if we take VGC data of all the units all Zelda games have sold, not counting spinoffs, (83.39) and divide by the number of Zelda games released (27), that gives us an average of 3.08 million units sold for each individual Zelda game. So, Skyward Sword is close to a million above the average.

If we look at just the 3D games, not counting remakes, we get we get 28.26 / 5 = 5.65 million units sold. In that case, Skyward Sword was disappointing, but the ony 2 games who sold above that mark (Twilight Princess - 8.75, Ocarina of Time - 7.60) sold WAY above that mark. 
Otherwords, I think they were satisfied with Skyward Sword sales wise.

Want to know what happens to OoT Link? 
There are hints of it in Twilight Princess. But I wouldn't mind another game in that part of the timeline. 

I don't think we'll see the last of this kind of Zelda, nor the old style either. I think they'll go back and forth between the 2, depending on the scope of the game, or just do something different again. With Nintendo, we'll never for surely know.

I could see them doing at least 2 Zeldas per system, (kind of a stretch seeing as how Breath of the Wild was the Wii U's only game and it took its entirely lifespan for development to finish), where the first game is a huge, open-world/sandbox type game like Breath of the Wild, and with the second, they want to kick it back and take it easy by reusing the first games assets and engine with the second and make an old-school Ocarina of Time styled 3D Zelda. That, or we get a top down 2D game. Though I certainly wouldn't complain about getting all three for one system.