Edit: sorry if I missed some answers, took longer than expected to write this whole post.
For your first paragraph, of course that makes sense, but your original reply had nothing to do with mine. Hyrule Warriors is indeed a different series, in a different genre, appealing to different people (the usual Warriors spinoff goal being to attract other franchises fans into Warriors gameplay, and Warriors fans into other franchises), but it doesn't mean that publishers don't look at the feedback to create other stuff. Fans loved the many female characters available in HW, Miyamoto talked after that about a Shiek spinoff. It's likely they are trying little by little to see where they can go, with HW being more of an hommage, and thus with less risks than directly trying another action-adventure game (but more action focused for example).
I completely agree on Aonuma's excuses being bad, but he's not trained for that. It's the equivalent of that stupid Ubisoft guy saying female character models were hard to animate as the reason of AC not having a female playable character. Miyamoto doesn't care since nobody will dare blame him for whatever he says at this point. Reggie or Bill, being in PR, would probably give better excuses while being as vague as possible.
Fans can obviously have their opinion about characters, but that's the thing, casual fans and regular players won't. Those are the hardcore fans always complaining about something (right or wrong), be it gender issues, timeline stuff, gameplay not being exactly like they wanted, X companion talking too much or not enough, etc. When your series has been popular for thirty years, you have to find the right position to be able to appeal to both without compromising your game's formula either (which was kind of Sonic's problem).
So, again, for Link, this is a bigger risk than 25 years ago or so, since they've followed a template for a long, long time and basically established this character (again, without him being "technically" established at the same time) and the game's genre (this is not an RPG where it's easier to switch after a while). This point mainly applies to having a female Link or a new character being playable, or even a less known/popular one (like Impa), not Zelda herself. Zelda herself, on the other hand, need a change of portrayal and to start being more popular, which is another problem that they have been trying to solve over the years, especially since they went 3D (Spirit Track, Sheik, Smash, Hyrule Warriors, Tetra...).
Of course they are interested in having more sales, but in this case, having a defined character is not seen as the problem (same for Mario or Metroid), the problem was using the same formula in terms of gameplay (which is the most important thing for Nintendo).
You can rightfully argue that this wouldn't change anything in terms of gameplay, but that is the issue. Why should they do it when they have a well designed character in a thirty years old franchise? Why put Zelda playable in a main game when it is supposed to be about Link?
The best you could expect in the next decade could be some switch at some point, like Ciri in Witcher 3 (it's still very much a Geralt game) if you truly want to force into the main games, but pushing Nintendo for a true spin-off in a similar genre with a strong female protagonist is actually the best thing to do and the only thing that they will accept (for better and for worse). They are perfectly in their right to stay with Link since, once again, they have other games (a lot) catering to other expectations.
You mean like in Super Mario 3D World? You're probably referencing this, which was focused on multiplayer.
Another Mario Galaxy or Sunshine, aka focused on single player adventures and a bigger story "focus" (for a Mario platformer I mean), they very likely won't allow this choice. Apart from Luigi obviously, since he's basically just an easy interchangeable copy of Mario (and I don't mean only in a gameplay sense).
My original reply did have to do with yours, unless you're referring to a different post... ?
And they know now, more than ever, that there's demand for it. They've known there was demand for playable Zelda for ages, and the notion that a playable Zelda necessitates different gameplay from the main series is a fallacy. And none of that addresses that people want playable Zelda in a mainline Zelda game, and the spinoffs your prop up don't have the same appeal. That's the problem that's not being addressed.
Girl Link and playable Zelda don't compromise the formula, certainly no more than boats, trains, crafting, cooking, etc. And considering this matter has been reported on at The Verge, Forbes, and other really mainstream, non-hardcore video game-focused sites/publications, it's not merely a "hardcore" matter. Anecdotal, but my girlfriend isn't a hardcore gamer doesn't play Zelda, and doesn't follow game news at all, and still said Link looked like a girl at the Zelda U reveal, and knew Link was a different person in every other game. It's worthwhile for Nintendo to learn to address these matters in modern times. Don't see how any of that is excusable or acceptable — it being understandable doesn't make it okay.
"Why should they do it when they have a well designed character in a thirty years old franchise?"
Because fans want it, and it'd make a statement about how girls can be the chosen hero, and girls don't have to be relegated to princess-status. It would fit within the existing lore of the series easily and would reinforce the notion that courage doesn't require being a boy. It would also reject the notion that tradition is a good enough reason to keep things from changing when that's not true.
What about that androgynous character design being remade as a girl would make it poorly designed?
"Why put Zelda playable in a main game when it is supposed to be about Link?
Because there's nothing bad about having a mainline game be about Zelda when the series is named The Legend of Zelda, and people want it to happen.
What value is there in telling more stories about Link when Link has been presented as little more than a blank slate meant mostly to be a connection between the player and the game throughout the series?
They're well within their right to keep things the same, and fans are well within their rights to call out their poor reasoning, and their adamancy to perpetuate the idea that gender is intrinsically tied to courage, heroism, etc., intentional or otherwise.
And Super Mario Bros. 2 had Peach, Luigi and Toad playable and was a single player game. Along with 3D World, yes.
Luigi being mechanically similar to Mario in the Galaxy games is just more evidence that you can have different characters in these games and still be functionally the same experience. A girl Link wouldn't require different gameplay, and there's nothing in this fictional world that a girl Link couldn't do that a boy Link could. What was your point here?
I get that it was possible and now it's not something on the table but their decisions haven't violated any spoken or unspoken rule of the series. I understand fan disappointment in not getting something they wanted. The reaction seems overblown and I think people are being silly nannies about it. Of course, this is all about my opinion and debating about it won't get us very far.
That Zelda point is a more interesting debate and I suspect that it might be a gameplay issue that Nintendo hasn't wanted to address. Zelda gets things done a lot differently than Link.
It still hasn't been outright explained why it has to be that way, at least not in a way that makes sense within the lore. The Triforce balance stuff really, really doesn't make sense and seems poorly thought out.
Outside of the lore, it's just them wanting to keep Link the main character without much more reason given. A lot of people don't agree that such options/changes would affect brand recognition or anything like that, and Miyamoto has just shot down possible playable Zelda, as if it's just a given that such a change is out of the question, even with a reincarnating main character.
SLU is a dlc campaing starring another character, not very uncommon, Luigi is a spin off series.
the number of Zelda spin offs is low (after all, Zelda is an adventure series unlike Mario)
but it did got Tingle, Tetras Trackers and Hyrule Warriors with Zelda herself playable.
then you have to think how many Mario spin offs had Peach as the main character! i think only the DS game.
How many stages were in that DLC?
And those spinoffs for Zelda don't play like the mainline series, which was the point I was making
Female Link is and always will be a terrible idea perpetuated by people who'd rather have a man dressed as a woman as the heroine than see Zelda finally get her time in the spotlight. It's stupid and its proponents are more rabid than rational.
That said, I'll never say no to a game that lets you play as Zelda as much as some Marios let you play as Peach.
They're not letting Zelda get her time in the spotlight either — you'd be better off supporting girl Link as well as playable Zelda since Miyamoto is opposed to both.