Even if the box theory turns out to be true (it may be, it may not-- it's impossible to say definitively of course until the game is released), it's still hasty to say this proves Ken and Incineroar. Just because the rumors (Verge) has implied this, I wouldn't want to put all of my stakes in them. For example, he didn't necessarily predict K. Rool, right?
Based on the theory, I would definitely say that Ken makes the most sense (Zack Fair or some FF swordfighter would be an awesome echo for Cloud though), but that's mainly out of speculation not based on rumors. As for the last newcomer, just because Verge said Pokemon newcomer, doesn't mean it's actually a Pokemon. In fact, I actually don't think we're getting a Pokemon newcomer (as base roster anyway). I would think it would be someone like Geno or Skull Kid (a popular character fans wanted forever), Tails (based on this theory, Shadow isn't an echo, so that leaves more room for Sonic reps), or Dixie Kong or someone from a newer franchise like Elma.
Of course, this is all speculation and fun and games. If all of these rumors do happen, I will happily play as Incineroar. As it is, I am already super hyped about this roster, and I honestly think this could be the best Smash game to date. As it is, this roster-- and more importantly, this entire game-- is exceeding expectations. Maybe I'd love to see my desired characters, mainly Dixie and Tails and Geno, but as it is, this game is a game for the fans, and I'm already in love with the game modes as well (Tournament Mode!!! Smashdown!!!). The point is, no matter what happens, Smash speculation is a once in a blue moon thing, and I'm enjoying every second of it!
The game is a lot more than just the roster anyway and as it is I'm probably just going to main Pikachu anyway no matter what hype inclusion we get