Alright, once more over the facts and then I'm going to give up on the people who just want to be ignorant in the hopes that (insert character name here) will be a newcomer...
1. When a leaker leaks something to someone outside of the company, we have no idea how "fresh" the information is, nor do we have any clue what the state of the roster was at the time the information was delivered.
However, we DO know that there are a number of good reasons for a leaker to not leak everything they know until later. Aside from generating tension/hype, it's also a good way to protect their source on the inside.
How does that work?
-Someone inside the development team of SSB4 leaks a partial roster of newcomers to Sal back before E3 of last year. They do this with the caveat that Sal not release all of the information until the time it will be released anyway draws near.
-The leaker asks this of Sal because he or she knows that, as development time goes on, more and more people inside the company will know about the information anyway.
-At the time the information was given to Sal, the leaker could've been 1 of only 10 people to know this information, and would've been relatively easy to weed out.
-But when the information is released the day before it's announced, the entire dev team of 200+(?) people likely knows all about who the newcomers are so it's very difficult to say who leaked the information. This protects the leaker from being found out.
So when Sal got his info, he could've known about just this list of newcomers and he could've known that a Pokemon from X/Y was going to be in but the dev team had yet to decide on which. It's also extremely likely that he didn't get the FULL list of newcomers since it's highly possible that list wasn't finalized, nor was he certain when and where the known newcomers were going to be shown because that too was likely in flux. Rosalina might've been decided upon after he got the leak and, again, it's fully possible that he hasn't had ANY new information since, but has been releasing the information he DOES have over time so as not to blow the cover of his leaker.
Remember, Sal got the villager right DESPITE Sakurai saying that "Animal Crossing isn't violent enough" for Brawl. His "prediction" went DIRECTLY against what we previously knew from Sakurai's stance on AC in Brawl (and as we all know, it's possible for a game to have a stage without a playable character to go with it).
Then, he got WFT right, which, up until that point, no one even considered the WFT a candidate for a character.
To go AGAINST everything we knew about Sakurai's stance on Animal Crossing AND to pull a character like WFT out of the blue when no one considered her? Sal would have a better chance of being attacked by a shark that's being struck by lightning while it also won the lottery.
Bottom line, Sal got a leak. Will he get another one? Who knows, but he DEFINITELY received some very real information at one point and anyone who believes otherwise is ignoring the obvious facts at this point.