Veterans:
Luigi, Ganondorf, Falco, Mr. G&W, Marth, C. Falcon and Ness - Obvious mainstays, believing any of these to be cut is just stupid.
R.O.B - Unlike some I don't believe this guy will get cut, simple as that, I see no reason to cut him. If G&W could survive from Melee to Brawl, R.O.B will survive this.
Jigglypuff - I'd consider her to be cut due to her low priority in Brawl if it hadn't been for the recent announcement that she's one of the new Fairy-types in 6th Gen, not only allowing her to get a revamped moveset, but also making her eligible for minor advertisement.
Meta Knight -He's unlockable because 1. He's not as important or recognizable as Dedede and 2. He has a very badass image that allows him to be a very cool character to unlock much like Mewtwo in Melee.
Sonic - Sakurai wouldn't have gone so much out of his way to include him in Brawl just to boot him off in the next game. So with him being the most requested character in Smash Bros' history, and Nintendo taking Sega under their wings tightly, there's no doubt he'll be back. On the other hand...
Snake - This is a tricky one. Now people constantly say that Snake has no rights to be in a Nintendo All-Star anymore, but honestly, he's more relevant to Nintendo now than he was during Brawl solely because of a single 3DS release. Snake has never been a character faithful to Nintendo, but he got in either way, it's just a testament to the fact that Smash Bros isn't just one big advertisement for Nintendo. He's also so unique in playstyle, no one can mimic him, which is the kind of additions we know Sakurai loves. Plus, Sakurai says that no one's cut yet, so I believe he already has the rights to work with Snake and Sonic at the moment, meaning that they are in.
Mewtwo - Duh, duh and double duh. Mewtwo is the only character that was present in Brawl that I am more than 100% sure is in. While Little Mac is 100% in, Mewtwo is 150% in. Not only is he the single most requested character, but he's a lot easier to work with since he's practically a veteran, and his new form will represent 6th Gen. Of course he's in.
Newcomers:
Mega Man - Confirmed. I believe he'll follow the path of Sonic and Snake and be unlockable.
Pac-Man - Again, I've chosen to go with the leak for this. Sakurai has shown interest in him too, when he was conversing with an interviewer about how Pac-Man could work, so I've heard at least, haven't read the actual interview. Even then he's never been a very unlikely addition, just not a very wanted addition.
King K. Rool - Serving as the single newcomer on my roster who will not be revealed before release we have K. Rool. I was on the edge whether to include this guy on the starting roster or Ridley, but went with Ridley. King K. Rool has pretty much just as much support as Ridley has over here, but to his favor he is pretty much equally as popular in Japan too. So why unlockable? Well, firstly, as much as we love K. Rool, a random bypasser who isn't a Nintendo fan will probably just see him as some fat crocodile. That doesn't sound so appealing, does it? Everybody loves dragons though, so with Ridley being a starter he can be on the box art and be used as general advertisement. Of course the general Nintendo fan will disagree with K. Rool just being a fat crocodile, I heavily disagree with it too, but that's how the general mass would view him on first sight, and if they don't view him like that they're likely already Nintendo fans. K. Rool is also the kind of character which is great to leave as an unlockable just to cause tension in the fanbase about whether he's in or not, given that he's been excluded from the DK series for so long it'll be an ingenious way to create hype. So either way, K. Rool over Dixie because Smash Bros is more than a cheap advertisement, that's one reason why Dixie's role in Tropical Freeze and K. Rool's absence in it doesn't matter. Then there's of course the thing with K. Rool having potential to be more unique and he's much more distinct than the rest of the DK crew. Most of you likely know the tons of great reasons to include this great character, so I'll move on.
Cuts:
I'll explain this very briefly. I tried to show no bias here, so two characters I love had to go, that being Lucas and Ike. So yeah let's just go over it quickly.
Toon Link - Cloniest of clones, easiest cut, would be missed as much as Young Link.
Lucario - Not putting him here because of Mewtwo, putting him here because as a veteran he's far less important to a Nintendo All-Star than any other character mentioned in this post.
Lucas - He's a semi-clone, and he's Japan-only, meaning less people will get hurt by his cut since so little people have a relation to him.
Ike - FE is a flavor of the week franchise, and with Ike's time having passed I sadly see him getting cut as a very real thing.
Wolf - In Brawl he was the lowest prioritized character, and that was when he was a newcomer. As of now he's just the least popular semi-clone of Fox, and I can see him being even lower prioritized this time around.
Mind you, my idea is that if DLC is made available for this game, the cut characters will be the first ones to be downloadable.