I can't really say why I know this, or how I obtained this information, so I'm completely understanding if you want to take this with a grain of salt at best.
I know six characters yet to be revealed that may surprise you folks.
The first of the bunch? Dart, from Legend of Dragoon. Plays similar to a slower Link, if we're going to make comparisons to Smash Brothers. The second? Blasto, from the game of the same name. First step to gauge interest for a reboot. Captain Falcon clone. The third? Aya Brea, from the Parasite Eve franchise. Uses her 3rd Birthday character. New playstyle, not really comparable to Brawl. Fourth is Toan, who hails from the Dark Cloud series. Another Link clone. Fifth goes to Sir Daniel Fortesque, of the MediEvil franchise. New playstyle. And sixth, last but not least, is Spiderman, who uses his trademark blue and red suit. Transitions about as well as he could into the game, new playstyle.
I didn't know Sony was making the new Spiderman movie. Between that and his appearance in the Tony Hawk game I guess there is a very slim chance of him being in. He should definitely incorporate some of his signature skateboarding tricks like the Spidey Flip.