I really don't get people who cares about spoilers in a fighting game. I personally want to know more stuff as soon as possible.
Anyways, I really doubt Nintendo is going to reveal everything about the game prior the release to avoid non-Japanese people getting spoiled. I think we might get one or two newcomer reveals in the following twenty eight days, but that is about it. Another Smash Direct? I don't expect it to happen until the Wii U version is close to be released. While I doubt the Wii U version will be rich in content (various different modes and stuff) as the 3DS version, it most likely have some big exclusive mode like Smash Run, so a Smash Direct is needed to showcase it and a few other extra things that version might have. What I can see happening is a newcomer reveal in a (general) Nintendo Direct and another newcomer reveal one or two days before the release.
The whole roster will BE KNOWN with the release of the 3DS version. For those of you saying that Sakurai will slowly reveal characters up until the Wii U release and those revealed characters as free DLC would never happen. It would be unfair to those consumers who may not have an internet connection, and they can't be cheated out of their product.
It would be unfair to the people buying only the 3DS version also. We shouldn't be prejudiced simply because Nintendo decided to release the Wii U version after the 3DS version. We are paying for the game, so we deserve to have all characters in the game
in the release date, without the need for DLC shenanigans. The people who are going to buy the Wii U version only have to deal with this.