I'm fairly confident the leaked Character Select Screen features the entire roster, and that there is nothing left to unlock.
Think about it: Everything in the leak comes from video footage shown to the ESRB. Thus, everything has some bearing on ratings. Check these images again -- you have potty humor (Wario Waft), gambling (Spectator Mode), drugs (see "grass" in Training), T&A (Krystal, Candy, Barbara, Twinrova, Tharja, Tiki, etc), realistic weapons (the missile reference, possibly Bowser Jr.'s cannon), religious references (Devil Car, Demon King, etc), personal information (Miis, location), and more.
And the Character Select Screen? I think that's a chance for ESRB to see every character in the game. So they can know that the characters, in and of themselves, are nothing inappropriate.
As for the lock icon on All-Stars -- that could've easily had been recorded before the CSS was fully unlocked.
What do you guys think?
I agree, but the DLC theory seems plausible....especially with MK 8 happenings.