Note that this wouldn't be the first time Pac-Man appeared in a Nintendo game. The arcade-only Mariokart Arcade GP featured Pac-Man and Blinky the ghost.
CHROM: Fire Emblem Awakening featured a number of new characters, including Chrom, the leader of the pack and one of the two main protagonists. SSB Melee featured Roy, the main character of a Fire Emblem game released around the same time as Melee. He was replaced in SSB Brawl by Ike, who starred in both Fire Emblem: Path of Radiance (GCN) and Fire Emblem: Radiant Dawn (Wii). As such, I believe the logical conclusion would be that Chrom would take the place of Ike. Which is fine, since Ike is stupid and dumb and I hate him.
By the way, Fire Emblem: Awakening is one of the best games available for 3DS. I never gave it a proper review, so lemme think about it... 9.5/10. Now go play it.
MAGNUS: Those of you who played Kid Icarus: Uprising (3DS) should recognize Magnus, the beefy, gravelly fighter. Masahiro Sakurai (the director of the Smash Bros. series) also directed Kid Icarus: Uprising, so I can imagine Sakurai having the sway to get Magnus in there. If he's not playable, it's almost a certainty that he'll be an assist trophy.
If not Magnus, then there are plenty of other Kid Icarus characters that could make the cut. Like the Tempura Wizard. If there's a character more synonymous with video games than him, I'd like to see it.
DILLON: Dillon is the star of Dillon's Rolling Western (3DS) and its sequel. In the game, Dillon (an armadillo) needs to protect small old-west towns from giant rock monsters. While he is not nearly as famous as some of the Smash headliners, he is perfectly suited for Smash Bros. You can see what I'm talking about here. Rolling, slashing, and smashing. He's a perfect fit for the Smash universe.
Like Magnus, Dillon would make a great Assist Trophy if he is not chosen as a playable character. And if not, then well... whatever. Shut up. I don't care. Go away.
NESS: I would be completely appalled if Ness did not make a return to the new Smash. He's been a competitor since the original, and is one of the most unique (albeit, difficult to use) characters. While it's true that Earthbound is not as popular as Mario and Zelda, Ness is clearly familiar, especially among Nintendo fans. Plus, since Nintendo finally released Earthbound on Wii U, his name should be more known that ever.
Side note: I think there's a good chance that Lucas will not return. With all the new characters, they will probably have to make room, and Lucas is the best candidate to get the axe (and yes, I mean that in a violent way).
CAPTAIN FALCON: This one is a given, but it needs to be said anyway, given that he's the best character in the series. Captain Falcon combines speed, power, and a wicked-awesome punch to create the most beloved and most impressive fighter in the Smash Bros. pantheon. Between the Falcon Punch, the Knee of Death, and the Super-Hug, Captain Falcon has some of the best moves in the series and sports a sweet costume, to boot.
Sadly, I doubt any other F-Zero characters will make the cut. Despite F-Zero's immense popularity, Captain Falcon is the only racer to fight in the Smash arena. Samurai Goroh was a pretty good bet, but he has been confirmed as an Assist Trophy. I suppose there's still a possibility for Black Shadow or Jody Summer, but it seems unlikely. I guess people would rather see more Starfox clones like Falco or (barf) Wolf. Stupid people and your stupid F-Zero hating guts. You will see one day. When the machines rise up. In the future. At some point.
So what do you think? What other characters would you like to see? Tails? Poo? Knuckles? The guy from Dig Dug? Then leave a comment, ya dungus.