We have had the announcement of several characters over the course of the year for the new Smash Brothers and even just yesterday we had two new characters that have been confirmed. As we already know there are still a handful characters to be revealed for the game before the final roster, and we will know about all characters by the middle of next month.
Why is this you may be asking well apparently the Japanese Publication Coro-Coro is set to have a big story on the 3DS version of Super Smash Brothers next month, within this we will be able to see all of the playable characters for both versions of the game and also all the stages for the 3DS version of the game. The magazine releases around the 15th of each month and you can probably find leaks around the 12th.
I would imagine that we will find out the remaining new characters prior to this however through a Nintendo Direct or another form.