We're running out of space here for characters.
Let's take a look at the Gematsu's leak. It has eleven characters:
Villager
Mega Man
Wii Fit Trainer
Little Mac
Gekkouga (Greninja, but Gekkouga sounds cooler to me)
Pac-Man
Mii
Chrom
Palutena
Shulk
Chorus Guy
That's eleven newcomers. This leak is true, if Gekkouga's inclusion didn't make that clear. That's not to say there's not more out there; Rosalina is in (brings us up to twelve), but we are running out of space.
I'm sure we'll see Mewtwo and a retro newcomer (still going with my underdog choice, Mach Rider), which brings us up to fourteen (counting Melee veterans as a pseudo-newcomer). Assuming there is no Brawl veterans cuts, that brings us up to fifty-three characters; fourteen more than Brawl. And that's the same amount as Melee.
If a character isn't already confirmed, isn't in the Gematsu leak or isn't Melee/a retro character, then the only way we are going to see a potential newcomer is if Sakurai is gracious enough to add more than fourteen newcomers. That's not to say you should despair for characters like King K. Rool or Isaac, but do take precaution and not flaunt them around as shoe-ins. And cutting Brawl veterans will not magically give us more newcomers; that's not how reality works. One only has to take at the current status of the Ridley thread of the consequence of this.
still optimistic about King K. Rool, though.