8/24/2018
This is my prediction roster, much more based on who I think will get in rather than who I want to get in.
Echo Fighters
Shadow: Like most people, I believe Shadow will get in the game as Sonic's Echo. His Assist Trophy is not only missing, but Knuckles is featured as a new Sonic series assist. Not to mention, he's a popular character and this game seems to be focussing on popular picks.
Isabelle: Just like Shadow, Isabelle's assist trophy is not only missing but seemingly "replaced" by Kapp'n. Isabelle has also grown exponentially in popularity since her debut.
Ken Masters: Ken seems like the obvious choice for an Echo fighter, considering that essentially what he was in his debut. All they have to do is change the hadouken to be more firey, and he's basically done. (Obviously animations and what not would be changed but still).
New Fighters
Skull Kid: Another character who seems to be almost unanimously agreed upon. With his assist gone and the Moon there to replace him, he seems almost obvious. He's a popular Zelda character, and would be the first one not to be a form Link, Zelda, or Ganon.
Karate Joe: There was possible evidence found in Sm4sh's files for a Rhythm Heaven rep, and one has been heavily requested. I chose Karate Joe because he's popular, a recurring character, and could work really well as a unique fighter.
Elma: I used to think and support Rex being in the game, but I think he was created too late to be in the base roster. Elma on the other hand, would be perfect, and is a popular character.
Geno: From what I've seen, the three most requested characters in Smash history have been Ridley, King K. Rool, and Geno. We have 2/3, and Square Enix is already lending character rights. Sakurai has also been interested in him, and has wanted to put him in for a while.
Incineroar: I could see Decidueye getting, but I have a feeling its gonna be Incineroar. From what I've heard, it seems to be the most popular Sun/Moon started in Japan, and seems to the be the big one in the anime (Much like Greninja and Charizard).
Honorable Mentions
Impa, Heihachi, Ninten, Viridi, Hades, Rabbid Peach
09/15/2018
Blue = Confirmed Green = Predictions
Characters
Shadow: Shadow returns from my last roster, as an echo of Sonic. After Isabelle's reveal, I was heavily considering making him a new character. But I have decided to keep as an echo, because I feel like 3rd parties won't be getting two characters outside of Echoes. I'd happily be proven wrong tho.
Ken Masters: Ken also returns from the last roster, being Ryu's echo. Ken seems almost too obvious and perfect, that I'm almost guaranteed he'll get in.
Skull Kid: Another returning character, Skull Kid also seems heavily hinted at. With the Moon being an Assist Trophy, and the Evil Ramblin' Mushroom reversing players' controls, Skull Kid's two things have been replaced. Not to mention, the background of the August direct seems to perfect (especially when the E3 presentation seems to have hinted at K. Rool).
Isaac: Isaac is a surpisingly popular request, and I think it's enough to get him in. The one image that seemed too similar to Golden Sun's battles pushed him over the edge so I added him.
Geno: Yet another returner from my previous roster. This is another character I'm extremely confident in. He's massively popular with fans and even with Sakurai himself. With all the love Square Enix has been giving the Switch after the direct, his chances seem even stronger now.
Banjo and Kazooie: Alright, this is my least confident choice. All the Microsoft-Nintendo love going on, his chances seem pretty good. But, it doesn't gauruntee anything.
Cuts from Last Roster
Karate Joe: A Rhythm Heaven character seems very likely, but I'm not sure if it's happening. Still, it seems the most likely to happen out of the ones not on my roster anymore.
Elma: Like a lot of cut characters, Elma doesn't seem like as much of a heavy hitter as Geno, Isaac, and Banjo. Again, I would be stoked if she got in but I'm not feeling it as much.
Incineroar: At this point, I'm not sure if a new Pokemon is necessary. I have a feeling a new Pokemon character is gonna have to wait until DLC, and it'll probably be a new 8th gen one.
10/28/2018
My final prediction roster, based only on the Grinch leak. Not changing it until post game where I may do DLC predictions.
11/16/2018
Ooooof I ate it on the Grinch leak. That's okay, Incineroar and Ken both look AMAZING. Anyway, DLC predictions;
So Rex was almost there, but then I realized he wouldn't have made such a big deal about his Mii costume being a bonus for the SmashPass.
These all seem like choices Nintendo would choose.