I hope it's one of those and not the newer song they used in Squeak Squad.
So I noticed something in the "Characters" page of the Dojo:
Now all of this is just speculation, but ASSUMING that the starting line up for newcomers and vets are going to be an even 8 vs 12 respectively, to make the characters page even, then there are only two newcomers and one more vet to reveal. If that WERE the case, Captain Falcon is the only vet that needs to be revealed. It would also support the theory that Lucas is replacing Ness as a newcomer.
Which would leave just one more newcomer to reveal for the starting line up. Either someone new or Metaknight, if he ends up not being unlockable. Also, it means that Luigi and Jigglypuff are still secret characters, like in the last two games. Along with any other secret characters from Melee.
I don't know if I'm the first to post this or not, but I can see this happening. Then again, I don't know if Sakurai would actually plan out the roster to accommodate an evenly organized characters page of the website.