I'm honestly surprised that people have given either leak (both ToS and Smash World) much consideration. Granted, I don't pay much attention to Smash prerelease speculation, so maybe there's something I'm missing.
Dixie, Chorus Men, and Mewtow having trophies alone is enough to make the leaks incredibly unlikely. Sure, playable characters have multiple trophies, but these are usually marked in parentheses, like "Samus (Varia Suit)". Trophies from beating Classic just has their name, which is the case for the Dixie, Mewtwo, and Chorus Men trophies. That's enough to put the leak in the BS folder, I think.
The leak being more detailed and specific doesn't make it more likely; it could also mean that the "leaker" was taking a risk and adding in more details to make people think it's more likely, because hey, "if he was faking it, why would he add in more details and risk himself getting debunked?" Apparently this sort of thing isn't common in the Smash community, but there's been several fakers who've done so in the Pokemon community. Plus, keep in mind, this leak came from 4chan, where you can stay anonymous. If something came out to disprove the ToS, then he could just make a new tripcode, come up with another leak, and people would be none the wiser.
As for Spainkiller's source, I still think the trophy argument still applies to it. "Well my friend who works at Nintendo said" isn't enough to convince me that someone as anal as Sakurai would make weird exceptions to a few characters for no good reason. And honestly, while we don't have all the models datamined, we do have all the images and icons, and absolutely zero sign of any of these characters, yet according to his friend he saw them while working on the 3DS version.
I do think it's possible for the 3DS to unlock more characters via connecting to the Wii U, but it's not going to be anyone who already has a trophy, and it's doubtful that the characters are going to be a who's who of what the internet wants in Smash. Prepare for a character or two that'll make people upset like Duck Hunt or Dark Pit. Possibly Dark Duck Hunt to advertise Duck Hunt Uprising, heh.