I'll kinda get the feeling there won't be more characters and they already told us all 23 playable characters on the DOJO.
You could be feeling wrong
It would be very sad when they don't have Luigi Already confirmed by a Nintendo member by accident,
Captain Falcon Probably being in again since his icon was shown on the Dojo
and Ganondorf Main villain, the Bowser to the Link series, probably in with a new moveset and some more newcomers in Brawl. How can we be sure there will be more than those 23 on the DOJO?
Easy, we can know it by looking at the Japanese release date, which says 24th January. Therefore we can't be sure that there only will be 23 characters on the Dojo, I call Captain Falcon as the next updated character