That's just not substantial enough to act as evidence against Mickey Mouse not being the protagonist of the mystery installment. He is a person, human or humanoid, a bipedal, by the way, Mickey is an integral character to the franchise, and is just as connected to Xehanort, but we still know so little of Mickey's journey, which is critical to knowing how all these characters come together, and just why Mickey states Sora is the one to reconnect these pieces.
You're acting as if Mickey is some throw away person which he is not, and to that point, Nomura has referred several times to Donald, Goofy, and in that case, even potentially Mickey Mouse, as persons, or people. Unless those translations were wrong, then this one could be just the same.
Sorry, Days is easily the weakest of the franchise, and is where Square is starting to show the rough edges around Kingdom Hearts longevity, they keep pushing out small scale pieces, while retconing in more unnecessary characters (Xion). A Riku game is out, I just believe that flat out, I won't even debate it. He is not a backbone to the franchise, and we know his entire story, you're lying to yourself if you believe we have more to gain from retreading old ground, unless they retcon yet again.
We know enough about Xehanort to make him a credible threat and he's already been built up quite enough, if we so need to learn more from him, then have Kingdom Hearts III deal with that fallout, as it would make sense, were Xehanort to be the series final villain, that his history be revealed and further developed in the third installment, but even I see that as overkill, we just know what we need to. Like Palpatine, like everything has to be spelled out in every little detail.
Lastly, these are the reasons why I weigh toward King Mickey Mouse, he is a person integral to the franchise, while we still know so little of his journey, even BBS just barely touches on some of his aspects, and KH1 and 2 just reveal bare necessities. His journey to gain the key, the note, what all happened to him in the realm of darkness, did he come across other Keyblade wielders. On top of all that, his journey crosses with Riku plenty of times that if Riku has a story to be told, in could be done so in collaboration with Mickey.
I for one do not want to see another one off, throw away character, that is suddenly introduced and is now integral to the whole plot, you might then say it's there story, blah, blah, blah, they've given us five games, six if you consider coded (I do not), and integral character should have already been included.
Plus, why shouldn't Disney have an integral character to the franchise, someone with a greater history and understanding then these others, I would feel much more comfortable following Mickey, then someone like Riku, who I've never respected as a character, or some new one that pops up to still the light.