Twilight Princess sold 8.8 million units between Wii and Gamecube, you think Zelda U can get close to that?

Yes, if NX handheld and home console are playing same games, so Zelda U and NX port definitely can make around 7m. Zelda U port like NX launch title will have huge impact, and we already know legs of great Nintendo games.

I don't think Zelda has that much mainstream appeal left honestly, not in its current form anyway.

I don't agree, especially because Zelda U is Zelda like fans always wanted (Zelda with huge beautiful true open world) and like Nintendo already said it will be ultimate "Zelda expariance". 

How big is the Zelda fanbase though, these days? Series sales have been in decline since Twilight Princess.

And Nintendo saying its the "ultimate Zelda" means nothing, it's just PR.

We had only one 3D Zelda after TP that is best selling Zelda, and sales of Zeldas for 3DS are pretty solid.

Well that world of Zelda U looks to me like world of "ultimate Zelda". And definitely not just a PR talk, I expecting that Zelda U will be of the best Zelda games and they said that they going back to Zelda roots with Zelda U.

Are the all early Wii customers Zelda fans? No. Then your point is useless.

And this are VGChartz numbers. So, once again, because of this Nintendo asked for Twilight Princess.

Zelda was a launch title so a large amount of early adopters would have been which negates your attempt at a rebuttal, oh WW sold almot 5m so it's not a flop thanks for confirming your earlier claim as wrong.

"According to the last reported numbers provided by Nintendo, Wind Waker sold 3.07 million copies worldwide, far below the 7.6 million set by Ocarina of Time.^[59] Aonuma would later comment in 2007 that he was "convinced the reason the Wind Waker did not perform well was because of its toon-shaded graphics style. It was something that you either loved or hated, and there was nothing that we could have done about it."^[58] As a result of Wind Waker's poor sales, Aonuma decided that "the only thing we could do was to give the healthy North American market the Zelda that they wanted," which led to the creation of the more realistic The Legend of Zelda: Twilight Princess.^[57]"

https://en.wikipedia.org/wiki/The_Legend_of_Zelda:_The_Wind_Waker#cite_note-NWR_13087-57

"Let me backtrack a little. As I was busy working on the connectivity project, it wasn’t as though the Wind Waker 2 project that I spoke of earlier came to a halt. Not at all. As some of you know, at E3 2004, we unveiled the game that would become Twilight Princess, the realistic Zelda game, and we announced that it was developed by the team that had been developing Wind Waker 2. Actually, there was a reason that that decision was made at the time. At one point, I had heard that even Wind Waker, which had reached the million mark in sales, had become sluggish in North America, where the market was much healthier than in Japan. I asked NOA why this was. What I was told was that the toon-shading technique was, in fact, giving the impression that this Zelda was for a younger audience and that, for this reason, it alienated the upper teen audience that had represented the typical Zelda player. Having heard that, I began to worry about whether Wind Waker 2, which used a similar presentation, was something that would actually sell. In addition, because we knew how difficult it would be to create an innovative way of playing using existing GameCube hardware, we knew what a challenge it would be to develop something that would do well in the Japanese market, where gamer drift was happening.

That’s when I decided that if we didn’t have an effective and immediate solution, the only thing we could do was to give the healthy North American market the Zelda that they wanted. So, at the end of 2003, I went to Miyamoto and said, “I want to make a realistic Zelda." Miyamoto was skeptical at first. I was so focused on changing the look of the game as being the solution we were looking for without coming up with a breakthrough game idea, and he advised me that “If you really want to make a realistic Zelda, you should start by doing what you couldn’t in the Ocarina of Time. Make it so that Link can attack enemies while riding on his horse using the Wind Waker engine, and make your decision based on how that feels." This is something that went against everything that the staff had been working on and I expected to come as quite a shock to the team. Surprisingly, my entire staff was enthusiastic about this change, and the project on which progress had slowed was given a much-needed jumpstart."

http://www.nintendoworldreport.com/feature/13087/eiji-aonumas-gdc-2007-presentation-the-fate-of-wind-waker-2

Official words, unlike your baseless comments.

Try reading it yourself not anywhere does it say WW bombed, nowhere, you've posted an article that doesn't back what you claimed earlier about games flopping, 4.6m is not a bomb you're wrong so time for you to swallow the truth.