I'm surprised that you didn't pick this.
EDIT:
To contribute my guessing game into the fire, I'll go just more on some of the characters I think could come to the lineup
Pokemon Trainer - With the advent of Pokemon Switch, I can see this be the opportunity especially with them not having to worry about the line between 3DS and Wii U, to bring back Pokemon Trainer and to make more space with having Charizard and Lucario now with Pokemon trainer completely.
Champion Leader Zelda - With Champion Link coming into play, this may be an easy job for them to bring Champion Zelda from Breath of The Wild, and to revamp her fighting style to a more swordplay style while Link receives the Bow and Arrow seen in the trailer.
Viridi - Out of all of the smaller Nintendo properties, Kid Icarus has potential for a character like Viridi to come to Smash. She'd be a unique challenge for the team, and one that would actually not be surprising, considering she is already introduced into Smash via by the Palutena's Guidance and the Mii costume from Smash Wii U/3DS. It could also lead to interesting moves she can make, and to have a pseudo reset bomb as her final smash.
Crash Bandicoot - Out of all of the third party characters that could appear for this new game, Crash may actually make sense when you consider that he is starting to make a comeback in the gaming industry, and with rumors pointing to a new Crash in 2019, it may actually make sense to have him fight against Pac-Man, Sonic, Mega Man and Mario.