Since NDAs are brought up here a lot, I want to mention quite an interesting instance that went under many people's radar:
Back during the height of Smash 4 leaks and speculation Shulk's voice actor (Adam Howden) was fairly candid for someone who we now know had to be under NDA.
First, there's this tweet:
https://twitter.com/A_HOWDZ/status/502879692836597760
He was swamped with people bugging him about Shulk in Smash, so this alone is fairly blunt I think.
Then there was this:
https://twitter.com/Xenado_/status/503282499704066048
Adam favorited this post asking for a "super subtle hint" about Shulk in Smash. You can still see it in the list of likes. IMO that's pretty damn transparent.
However, this was not even a week before Shulk's reveal. But I still think it's something to keep in mind while we hang on every tidbit or rumor regarding the next four characters. I think of this a lot when I see people immediately assume a character is out of the race because someone who would have to be under NDA says something.