I personally believe the leak. People keep asking "why didn't he mention Rosalina?" The answer is that he only revealed six characters, not the whole roster. If the leaker had revealed everything from the get go, chances are he wouldn't have a job any longer. I'm sure it'd be pretty easy for Sakurai to pinpoint where a leak that revealed everything came from, but a leak that states 4 semi-easy-to-predict characters, one slightly difficult one, and one impossible one? That's not quite as easy to track. Also given that the leak came right before E3, and information was probably known by many people behind the scenes at that time, this kept the leaker even more safe.
Heck, we don't even know when Sal got that first leak, do we? Did he get it that day and posted his "predictions?" Did he get it a week earlier? A month? Maybe he received the tip way before E3 and the leaker asked him not to divulge that info until a certain time, in order to protect his job. At said time, Sal made a forum post just stating his "predictions," and after they came true, he made a statement about how that information was leaked to him.
I might have my timeline wrong. I wasn't actually paying much attention to these boards back when all of this was initially going on, so if I'm wrong, someone please say so. But this is how I envision it in my head.
Same goes for the second leak. I have a feeling Sal got word ahead of time, but again in order to protect the leaker's identity, he didn't report on it until just slightly before the direct, and due to his confidence in the leaker after the first valid information, he actually posted it on the Gematsu site rather than just a forum post.
These are my thoughts on the leak. I still believe it's accurate, but I also feel there's no way we're going to know until we have the game in our hands. Chorus Men most certainly will be an unlockable character, and as others have said, they're really the one character who can solidify this leak to a nearly confirmed status.