Well we should be getting more character updates soon. Since the starters for games like this are always shown in the advertisements, the entire starting lineup should be known by the end of December or early January, since Nintendo usually likes to start advertising their games in Japan around 3 weeks before release, unlike NOA who starts 3 days before release.
And speaking of the starters, we can now confirm that King Dedede is indeed a starting character since the first event on Event Mode contains him and Bowser. Well unless you have to beat the first event mode to unlock him but I doubt that since you play as Mario in the first event match. If King Dedede was unlockable it would have been in an event as Kirby in a Kirby stage, just like how you unlocked Ganondorf in Melee from playing in an event as Link in a Zelda stage. Because other then Ganondorf, all other unlockable characters in Melee didn't appear in any event matches until after you unlocked them.