I work at Bandai-Namco, specifically in PR regarding their various fighting-game series (currently I am involved in helping deal with some licensing issues regarding a popular manga fighter that Namco-Bandai is hoping to release in the West...), and have learned various bits and tidbits of early info from coworkers involved in the Smash 4 development. Nothing super-concrete, and all this info is subject to change, but here is what I have learned.
* The Anniversary of Brawl's release in Japan will have a special Nintendo Direct focused on Smash 4. I don't think it will have a trailer included, but I am not sure. From what my friends have speculated, it may just be a retrospective on the Smash Series as a whole with a sliver of new info released.
* Little Mac and Takamaru were two of the first characters chosen for Smash 4, both being classic characters that have since experienced a revival via Punch Out Wii/Nintendo Land and are fan favorites. They also represent West vs. East, which Sakurai is aiming for after the previous series strayed too much towards Eastern characters like Fire Emblem and Mother.
* King K. Rool and Ridley are also two characters that are being given priority as they too have a lot of requests. King K. Rool's design is said to have a new design that Retro contributed to (perhaps a new Donkey Kong Country is on the horizon?), and Ridley will apparently have a style of game-play that involves the evolution seen in Other M.
* Shulk, Dillon, and Ghirahim are currently set to be included, but they haven't been finalized like the four above.
* Platinum Games is interested in including a character, yet nothing has been finalized yet. Will probably be from Wonderful 101, but nothing is decided upon.
* Starship Mario, Giant Chasm (Pokemon BW2), Pushmo Park, and Cookie Country (Kirby) are levels that have been worked on.
* There's a second Yoshi representative who has yet to be introduced and will apparently be appearing in a new game coming out soon that Nintendo asked to be included. The rumored Yoshi Land Wii U? It's apparently Yoshi's new partner another dinosaur character. The name "Debu" has been thrown around, but I'm not sure if that's it's name or a nickname since that just means "fat" in Japanese.
Although I remember someone during Brawl pre-release who revealed Wolf and some other things (was it a female?) and we thought the roster sucked so bad that we didn't believe her. Did she come out of nowhere too?
In the meantime, I'm actually going to grab info like this and document it. This time I'm not playing around.
But for what it's worth he IS telling the truth about the word Debu.
"What reason can anyone give me to not prefer the annihilation of all mankind to a scratch on my finger?"