Pac-man has little chance. Just because he's made by Namco means nothing. How about the fact that the Pac-man game for the Wii U got canceled? Or the simple fact that Pacman can't fight. I mean he's even been in a fighting game before...piloting a mech...I don't think that would work for Smash. Not gonna happen.
Krystal has the greatest chance of these five, followed by Lucina as an alt skin for Marth. Of course, Chrom has a much greater chance, but I'm assuming he's top 5. I mean for crying out loud he has his own stage already, he's 100% going to be in.
I have Pacman at #11 for a reason, i'll explain about how he's here in a sec. Krsytal does have a great chance, but like i pointed out Star Fox isnt in the same era as it once was. 2 characters would be fine but if a newcomer does come, Krsytal is the obvious choice. As for Chrom, lets see where he ends up on my top 10 list, if he shows up (wat am i kiidding, its obvious he will )
Now for Pacman
1. It does help a little namco is developing the game, but like you said its not a guaranteed.
2. Snake was in the previous game yet no MetalGear on Wii
3. Sakarai is a spectacular developer. How many characters had no moveset from their games? Pacman looks like he cant fight but then again Sakarai made Star fox+Captain Falcon from scratch right? Heck look at Wii Fit Trainer/Villager/Ice Climbers/MrG+W/R.O.B. All them can fight, they didn't look like they could of either pre SSB introduced!
4. He's at #11, cuz i dont think he'll be in game either as much as others but this came came up http://gematsu.com/2013/06/wii-fit-trainer-joins-super-smash-bros
Its a leak before E3 stating 6 newcomers. Wii Fit Trainer, an unbelievable choice was confirmed! 4 out of 6 already!