Like I said, I'm basing this roster off of purported ballot popularity, relevancy at the time of proposal finalization, and presence during Smash 4 DLC.
Geno has been requested since the days of Brawl, and still has a cult following. Sakurai went out of his way to negotiate a mii costume for him, which means he is aware of this demand. He even wanted to put Geno in Brawl, so he's wanted him in the past. I feel like Geno is highly likely this time around. If he has a chance, it's now. Slime is possible, especially with the ballot, but I feel like Sakurai would go for Geno first. Sora's best chance is as DLC. Geno also doubles as the Mario newcomer this time around.
Monster Hunter is a highly popular video game series in Japan, and has a lot of fans here in the West as well. Again, Sakurai negotiated a Mii Costume for Smash 4. It makes sense that those negotiations could extend to Smash Ultimate. Monster Hunter also has had good presence on Nintendo consoles as well. Again, Sakurai understands demand and sees that Monster Hunter could transition into Smash Bros. I will give you Felyne though. I think a Monster Hunter representative is likely for a third party representative.
Again, Lloyd was negotiated as a DLC costume for Sm4sh. Lloyd's games Tales of Symphonia and Tales of Symphonia: Dawn of the New World, were important Gamecube games, and Lloyd was a somewhat popular pick during Smash 4 speculation. During the ballot Lloyd garnered a good amount of support, and I believe that between this and how close Sakurai and his team are with Bandai Namco gives Lloyd a very good chance. Heihachi was ruled out in the past, and both him and KOS-MOS lack the fan demand that Lloyd has.
Honestly I'd definitely believe that right now.