I've been taking a lot of notes on this and I'd like to post them here for who I believe are the MOST likely newcomers, both unique and echoes. As many have guessed, I will also guess 4 more unique newcomers are left, but I believe there may also be a fifth joke/classic character that I won't be able to guess. Anyway, here it is:
Geno: I think this one has been explained enough by other people, but I'll explain again. Geno has gotten nearly as much requests as Ridley and K Rool ever since Brawl was released. Sakurai has stated in interviews he is aware of the requests. Sakurai said in an interview he wanted to include Geno in smash ever since Brawl. Sakurai included a Geno mii costume in Smash 4 to make up for him not being in that game. Square Enix doesn't seem to mind giving Sakurai legal rights to use Geno considering he got to make a mii costume of him. Every third party except Enix and Namco, at this point, have 2 reps. Geno would be a perfect 2nd rep for Enix and would fit the theme of heavy fanservice, especially since Sakurai himself wants him in Smash.
Lloyd: Many believe we'd get Heihaichi as a 2nd Namco rep, but I don't believe that is the case. Sakurai said previously that he did want Heihaichi in Smash 4, but he couldn't come up with a good moveset for him in Smash and also that he seemed like a poor choice considering he dies in the most recent Tekken game. On the other hand, Lloyd is a sort of mascot for the Tales Of. franchise and his game is perhaps the most memorable and praised game in the series. In fac,t Lloyd's game was first on the Gamecube. Additionally, he has received so many requests that he got a mii costume in Smash 4. He'd be a perfect 2nd rep for Namco and also fit the theme for fanservice in Smash Ultimate.
Skull Kid: Zelda has been sorely in need of a cool new rep outside of Link, Gannondorf and Zelda for a while now. Skull Kid is perhaps the most popular villain from the Zelda franchise outside of Gannondorf and Vaati. In fact, I believe that Skull Kid is the most requested Zelda character to be added to Smash. He was heavily requested before he was deconfirmed in Smash 4. Additionally, there's now a "Moon" assist trophy in Smash Ultimate which mysteriously doesn't include Skull Kid. Skull Kid's absence is certainly noteworthy considering how popular he is among fans. There was also a Majora's Mask mii accessory in Smash 4. And perhaps the biggest point is that leaker LoZ18 who LEAKED the August direct, that different modes would be shown, and that K. Rool would be revealed in it (after having already leaked who would be shown at the E3 presentation) said that Skull Kid was strongly implied to be playable.
7th Gen Pokemon (Decidueye or Incineroar): Every smash game in the past has added a new pokemon character as a unique fighter. Additionally, Vergeben, who has leaked many things correctly about Ultimate, said that there will be a 7th gen pokemon playable who isn't Decidueye, Mimikyu (deconfirmed now to add credibility) and Lycanroc. He said that only one out of his sources have told him who it is and that they said it is Incineroar. He specified that he's not sure it's Incinreroar and doesn't want to say that until all of his sources agree on it. I believe Decidueye should be considered just as likely in the case that Vergeben's sources are wrong about him not being the fighter considering how popular Decidueye is.
Echo fighters:
Isabelle: Isabelle was leaked by Vergeben around the same time he leaked Simon (although admittedly a few weeks later). He said that all of his sources agree that she is playable but didn't specify if she was unique or an echo. Additionally, Animal Crossing New Leaf was one of the top-selling 3ds titles out of the entire library. Isabelle also got a mii costume in smash 4 (seeing a trend?), and has been mysteriously absent as an assist trophy in all of the smash ultimate trailers. Just today, actually, Vergeben confirmed on Reddit that one of his sources got back to him and said Isabelle will be an echo. I personally believe this is true, also, because she doesn't do a whole lot in her game and echo'ing Villager would make sense as she, too, is a villager in the New Leaf town.
Shadow: Alright, this one hasn't been leaked, but I think it's pretty darn obvious and apparently so do a lot of others. Shadow was one of the most advertised Assist Trophies in previous games and was even in the intro of Smash Bros. for Wii U, yet he hasn't been shown in any of the Ultimate trailers at all and isn't in Green Hill Zone either. Shadow would also make for an incredibly easy Echo fighter for Sakurai to include, and he is also oa highly requested fighter.
Ken (Capcom), Ms. Pacman (Namco), Zack (Square Enix): Since Sega and Konami would both have an echo figher, assuming Shadow gets added, it would only make sense for Capcom, Namco and Enix to get echo fighters as well. Both echo fighter reveal segments have only had gameplay trailers and no cinematic trailers, so I could see these being revealed at the same time. This would give each third party equal representation, and simply seem like easy options for Sakurai. I was a bit hesitant on Ms. Pacman, but that simply seems the easiest.
If anybody would like to add to my notes, go ahead. I tried to make multiple points for each inclusion, with only the last batch of echoes feeling like a slight stretch. The rest of the characters I feel are incredibly likely.
