I have a feeling if we are to expect to a trailer we're probably not gonna get K Rool or Krystal in those trailers. Now my reasoning is that if anything they'll be middle of the road or hidden characters and unless their main characters get shown in the trailer their chances go extremely down. The reason why the Brawl trailer worked so much was that it consisted of mostly faces of the brand with Link, Pikachu, Mario, Kirby, Snake, Pit, and Samus with the side characters having a main character so you can gain a resemblance or associate that character with it's origins series in Meta Knight and Wario. To have Krystal or K Rool just show up with Donkey Kong or Fox would just be weird. And to have those two be the first reveals compared to Pikachu and Kirby would also be a bit weird but it's not off-putting. Though I would put my money soundly on neither of those two showing up first in the trailer so i'd probably pull my finger from predicting K Rool and Krystal as the first few newcomers.
Now onto my predictions. I'm going to go with Ridley(Samus will probably be the female character that shows up(unless Pit shows up to confirm Paulentena) and we won't have a female newcomer like the previous years), Little Mac(Self-Explanatory), Paulentena(Only if Pit shows up), Takamaru(To do battle with Little Mac), and Pac Man(seeing as how Capcom has really thrown Megaman around i'd hardly think they'd put him in this game even if Inafune wants him in Smash 4). My outrageous pick though is gonna go to Mewtwo. I imagine that he'll be the second to last to Pac Man to appear, I imagine he'll appear in a purple aura with his intense eyes starring at you but he's surrounded in shadow so you can't really see and then BAM we get "Returning: MewTwo" and it's Mewtwo in his new look so that arouses some interest in the new Pokemon games while getting mewtwo possibly a new moveset so he and Lucario can co-exist.(even though their moveset similarities are really minor)