My opinion about this subject is a bit different:
Impossible:
Almost impossible:
Really unlikely:
Unlikely:
Possible:
Probable:
Likely:
Almost garanteed:
About cut, I really think that representation and already being cut are big factors.
I don't see why bringing Ice Climbers back should be more probable than Charizard or Wii Fit Trainer.
I don't know what you thought when doing, but I tought about what would be the most obvious choices to go if they chose to do "Street V way" (I forgot the term, "pay for service ?").
Mario being top1, even if Luigi is a "shoe-in", if they must chose 10 characters, they would go for representing franchises.
As soon as the most famous got in, then Luigi, then the most famous side characters and second-tier main characters.
As a Smash complete game, ignoring DLC, everyone until "Unlikely" will probably make it.
Unlikely still very hard to let go. Ike is a example, just too famous and wished to be dropped at this point.
Rosalina, Wii Fit (main character of a third tier franchise)... but they are characters that I can see arriving later at the game.
I also thinks that the unique character that is really likely from the third-party characters is Sonic.
Even Megaman, you know... they would love to have, but would they fight for it ? I don't know.
Sonic on the other hand was the first third party for a reason.