One thing that sticks out to me about this is that the post just sort of...showed up in a thread about another "leak." On the eve of E3, I decided to dig through GameFAQs out of boredom and found a leak discussion thread. I dismissed it as fake and continued to read further into the thread, at which point Loz18 appeared and mentioned, among other things, Zelda's ALBW design. It's like he decided to post in the thread just to be like "uh, no, I'm right, look at me." We all know he went off the deep end after E3 and I realize that this doesn't prove anything, but I could totally foresee someone wanting similar attention and spilling all of his knowledge in a thread about a completely separate leak.
Actually, now that I think about it, I have to wonder how this 4chan poster obtained so much secret information at once. He claims to know of not only the roster, but also bosses and characters who got cut in the middle of development. Exactly how many people would be privy to that information? Very few, I'd assume. Papagenos' source apparently heard whispers of all these characters, but the sheer amount of info here gives me pause.