@runa:^Wakana wouldn't be the first person to "fight" a problem by denial, and, in my opinion, YK, the utahimes and the band sure see that something different is going on with her, but don't say anything because of "Japanese politeness", so to speak - they may find it rude to "meddle" into other people's business like that. Obviously, all of this is just supposition, just me wondering about it.
About sending the letter, I see that letter as I sign of our concern for Wakana's well-being, which can be proved in how many pages we spent trying to make it sound the less rude possible, since it's such a delicate subject. Just like some of us may be seeing the worst case possbile about Wakana, you, runa, and BS are doing the same by thinking that the letter would be interpreted in the worst possible way. Hopefully it wasn't.
@BS: the problems my friends may have with you or someone else are not mine. If you say that I'm biased because of my friends, that's not true because my intention here isn't to defend anyone; all I'm doing is showing my arguments about Wakana's case and pointing out that what was going on smoothly is now almost turned into a fight, because Equal came here and bursted out about how annoying this "bullshit" was, and when his post was decomposed as the nonsense it was, then came you to join him, making this about the "fight" between users instead of the discussion about Wakana it is intended to be.
Also, I never said you said anything about your adoration for YK. It is implied in the way you write. And, as I said above to runa, you are seeing the worst outcome possible to that letter. Continuing your metaphor, I think of the letter (and I hope it was taken) as, let's say, the philosopher suggesting to the surgeon that he could do better if he gave his blade a sharpening. This may have been a bad metaphor by me, but my point is that my intention, and of everyone who sent that letter, was the best possible, because we care about her. We weren't saying in anyway that she can't sing. It really could be misinterpreted as you're saying, but we hope that it wasn't. Who knows.
@Vert: I don't know what they would do, but I wish they would do something, even if it would prove me wrong. I'm concerned not only about her performance, neither would I ever expected anyone to be perfect at anything; but if she is really having any physical condition, I wish she looks for help and do what it needs to get better, be it having a temporary hiatus, be it retiring for good (may God forbid it's anything that bad). Also, I wouldn't really care so much if it was only a change in her tone, but it seems to me that it's indeed something more than that.
@Kawohni: that was what I and others thought at first, around two years ago iirc. I acknowledge that she isn't great on stamina, but it seems that she gets more easily tired with time.
Also, I understand what you say about her tessitura, and I agree with it. i think that Kajiura does put her out of her comfort zone - one example being Materialise live. I don't understand why Kajiura gave her the main (and high!) melody for most of the song, when it's clear that Yuriko can do it with a lot more ease.
@Equal: that may be right about her veins, but I would think a thinner person would sweat less. And to me, it seems that she is sweating more, instead. I don't know, though.
And yes, this discussion will keep going on until anything is said/done about it; until comes an official note about it, all we can do is theorize about it, be it the worst or best theories. But we can keep it a "discussion", without turning it into a "fight" every now and then.
About the pics: I admit, I'm bad at this, but to me it doesn't look like she is that different. Maybe the difference in her hairstyle, from roundish-short to long and straight, helps to create the impression that she is thinner. I'm not saying that it's totally wrong, though.
Maybe you just mean she's a bit fatter, but I gotta be honest, she's still really slim! 
