Like many others here i've been checking the official SBB website every Thursday for the latest character updates etc.
Meanwhile the official japanese website has been bombarded with all kinds of information by director Masahiro Sakurai.
Thanks to a member of the smash world forums we now have a translation for the information Sakurai has revealed.
Not all characters from the previous games will return. Any non-Nintendo character must have appeared on a Nintendo platform before; the tentative number of non-Nintendo characters is 1 or 2 (Snake not included). Our guess is that other character will come from one of Nintendo's closest third-party developers: Namco, Capcom, or Sega. Sakurai, noting that Smash Bros is popular worldwide, does not want the title to feature characters that are only popular in Japan (though given the success of Fire Emblem, that may change).
The speed of the game will be "moderated" (the translator guesses this means a slower pace). Every character's moves are being refined so that a player has "more freedom" in aerial combat. "This time, we'd like to stress easiness over the small details of combat, so overall it might become somewhat easier."
There are no plans for an online ranking system (although win-loss records might still be recorded). It does not seem that Sakurai is placing high priority on an online system.
Sources: 1up.com + joystiq.com