(Content Warning: Somewhat pervy pictures of human and non-human female trophies (supporting the story that this is the ESRB video), spoilers for StreetPass Plaza: Monster Manor and Kid Icarus Uprising.)
Pittoo and Wario are confirmed now.
All-Star mode seems to be locked in this picture, which may imply that not all characters were unlocked in the save file used to make the video. The leaker has apparently said they can't confirm whether or not that character select screen shows the full roster. (I would think the ESRB would want to see all the characters, but maybe not? The ESRB is definitely a lot looser than European rating groups where they have to play through the entire game themselves first; ESRB just asks for a video of highlights of the most objectionable stuff.) But it might not mean anything; the footage is all edited together anyway, and also there might be different conditions for unlocking All-Star this time.
There would be room for five more characters on that screen, assuming that Mii Fighters are under the wrench icon (this would make sense, especially considering we never got a "Mii Fighter Faces Off!" newcomer splash screen; Mii isn't a fighter, it's a customization mode).
That original list of DLC characters (Wolf, Snake, Lucas, Ice Climbers, Chorus Men) was confirmed to be made up. There were a couple of leaks before this one that listed Bowser Jr., Shulk, and Duck Hunt Dog along with Dixie, Ridley, Mewtwo, Chorus Men, and Mach Rider, and there's also a rumor about Impa now. (Chorus Men are looking least likely at the moment, taking it down to those five) Also rumors that every character has 8 colors/costumes, and Bowser Jr.'s other seven costumes are the Koopalings. Ice Climbers are looking really doubtful.
If the 48 characters on that CSS are it, I'd be happy. That's already a really good roster. But I'm really hoping for Dixie, Ridley, Impa, and Mach Rider. They make sense -- Dixie and Impa have been in lots of games in their serieses, including recent ones, Ridley should have already been in, Mach Rider has gotten a decent amount of acknowledgement in past Smashes, and would also help make up for losing Ice Climbers. Dixie and Impa could be modified clones of Diddy and Sheik, and together with Mach Rider (Snake clone? Wario clone? Would she be on her bike the whole time, or would they make up an on-foot moveset for her like they did with Captain Falcon?), the three of them would go a long way toward tipping the gender balance of the roster. As for Ridley, we've been left with just enough room for hope for months now. I don't think Sakurai would do that all the way up to less than three weeks before release if he wasn't in. The closest he's done to that was the Greninja trailer where he kinda looked like Mewtwo at first, and that only left us hanging for a few seconds, with the reveal being "You thought that character was playable... but instead it's this cool new one!" With Ridley, it would be months of buildup for a reveal of "You thought that character might be playable... Nope!" They've always been very clear about when a character's not playable, but with Ridley, all we've gotten are two times where he was indirectly implied not to be, without even using his name (and the animation on that Ridley shadow always looked more like a player-controlled character than a preprogrammed boss character to me anyway).