I wouldn't really consider Punch Out a full fledged fighting game.
It is a fighting game in a sense yes but honestly you're very limited to how you control Little Mac.
EDIT: Also just considering that, I honestly think that Little Mac has more of a chance at being playable than Skapon or Ryu. Honestly I can see where Sakurai doesn't characters from fighting games like Joy Mech Fight or Street Fighter respectively, so in a way he's emphasizing on characters that already have a moveset of their own in their games.
It is a fighting game in a sense yes but honestly you're very limited to how you control Little Mac.
EDIT: Also just considering that, I honestly think that Little Mac has more of a chance at being playable than Skapon or Ryu. Honestly I can see where Sakurai doesn't characters from fighting games like Joy Mech Fight or Street Fighter respectively, so in a way he's emphasizing on characters that already have a moveset of their own in their games.