Pac-Man - Come on, Mario, Sonic, Mega Man, developed by Bandai Namco. Will Sakurai pass this up?It's very possible, yes. Hopefully he does too.
Chrom - Marth is the poster boy veteran, both Roy and Ike are outdated. The only ways I can see Chrom being excluded are if Ike and Roy both return or if another Awakening rep is favored (Lucina, Robin) Ike and Roy are outdated,hmm sounds like another recency argument, hold me back people, Let me at 'em!
Little Mac - Also has retro value, one of Nintendo's unrepresented franchises that had a revival. (just like Kid Icarus)Okay
Mii - Would make for a unique addition, used in plenty other Wii/3DS games, and after WFT I don't think anyone would put this beyond the realm of possibility. No, just no. Please no.
I don't think every veteran will return, like I said it would be strange to me if Roy and Ike are both in. I have very little hope that Pichu or Doc will ever see the light again either. Mewtwo though, along with Lucario, may get their Mega forms included. Of the Brawl cast, I think the least likely to return is ROB.How is ROB the least likely?! Alright, I'll admit, he's as unlikely as Mr.G&W
Since Sakurai dropped that hint of Ridley being a hazard awhile back, I only expect him to show up as a boss (again). Same with K. Rool. Oh, hex no. I also expect the likes of Waluigi and Isaac to be doomed forever as ATs, and Shulk, Custom Robo, maybe even Paper Mario as well. Shulk? Assist Trophy. I shall laugh in your face.
I don't expect Palutena to be playable, but I won't be surprised if she is. Sakurai doesn't like to over-represent his own work, remember? After the addition of MK and Dedede, though, it's hard to say if KI will get another rep. Pretty much my stance on this.