Personally, I see these as our top contenders (in no particular order): Isaac, Geno, a Pokemon, Bandana Dee, Paper Mario, Dixie Kong, Skull Kid (maybe), Impa, Ken (maybe), Shadow and Shantae. Runner-ups: Banjo and Sora.
Of these, I think Dixie, Impa, Ken and Shadow are echo fighters. Examining the rest of them (please don't be offended if you support one of these characters; I'm trying to remain objective):
- Are Paper Mario and Geno going to vie for a spot? Who knows, maybe they'll both get in or be considered against the other. If the latter, I'm thinking Geno has more evidence in his corner but I can't deny that Paper Mario would be more relevant. Could be a bloodbath here.
- Relevancy isn't an issue if you're a retro or a significant character in your still alive franchise (ala K. Rool) but I would say it's definitely a factor if your series is dead (Isaac). Not that he can't be revived but Nintendo is going to have to make that decision. Will it be worthwhile to them? We'll see.
- Bandana Dee has tons of marketing and amiibo cross-compatibility (could have hinted at Daisy prior to her reveal) in his favor so I think he's pretty safe. I could make a dig at him being "Player 4" or a "Hat Goomba" or "Sakurai bias" but I don't think any of them are strong enough to go against him. It might even be beneficial this time around that his moveset would be on the simpler side if they're shooting to cram as many favorites in this game as possible.
- A Pokemon is a given. Sakurai is not going to ignore the votes for Pokemon in the smash ballot. I really hope that means we'll get an older gen pokemon this time and exclude the newer gen since I think there are better pokemon to pull from from older generations (no offense to fans of the newer games). Who that is, who knows?
- Skull Kid had virtually no presence in the ballot, as far as I know. Maybe Sakurai will want to do right by the LoZ series and add him in, as he is highly marketed (well, Majora is) and super iconic, but if we restrict things to the ballot, I think he flops. For all intents and purposes, we have two "leakers" going against each other right now for him too (with LeakyPandy staking their reputation on the line to deconfirm him as a boss character and loz18 being BTFO'd with this Direct). He would be a cool addition, is certainly iconic and is heavily marketed but.... no ballot presence and non-intuitive moveset potential could be death nails.
- Banjo has a super tall mountain to climb: 1) you have to get Microsoft on-board, 2) they have to be willing to revive his franchise since his franchise is currently dead, 3) you have to resist the temptation of grabbing someone else instead (like Master Chief or God help us, Steve; could be a Cloud over Geno situation). He no doubt did well on the ballot but let's be real, he probably wasn't #1. Anything short of that means he's mountain climbing. DLC maybe?
- Sora is owned by Disney. It's as simple as whether or not Sakurai wants to put "Disney" on the front page of the Smash website and he would have to. Plus, they'll probably want (a lot) of money. DLC... maybe...?
- Shantae, frankly, has zero clout. She's an indie darling, but there are bigger icons even in the indie scene (Minecraft, Five Nights at Freddy's, Undertale, even Shovel Knight). Unless she absorbs the votes for indies and is prioritized for her history with Nintendo and receives high marks for her design viability, she has a mountain to climb. Admittedly, it's not as bad as Banjo's mountain, though. On a negative note, hopefully she's just a regular trophy (or Sakurai says screw it and includes ATs as characters) so she can have a shot at DLC. As long as she doesn't get relegated to the snow globe of death, she has a very strong shot of coming in later as DLC. Few characters can compete with Shantae when it comes to the ballot, I'm sure of that.
So we could potentially have 9 uniques (if you're super optimistic), 7 uniques (if you exclude Banjo and Sora) or 3 uniques (if you're super pessimistic and exclude: either Geno or Paper Mario with the other getting in, Skull Kid, Isaac and Shantae leaving only Bandana Dee, a Pokemon and either Geno or Paper Mario as the uniques). I read somewhere that 4 clones was equivalent to 1 unique character in terms of development so you could wrap those previous 4 echoes into 1 and consider that a "slot".
Examining the previous Smash (prior to DLC) we had: 15 uniques (if you count the Miis separately, 13 if not) and 3 clones (Dr. Mario, Dark Pit and Lucina) so you can count that as... eh... about 14 slots (if you want to split hairs with the Miis and include the clones; they did all require development time).
Right now we have (including veterans; I'm going to consider "semi-clones" unique even though logically they would take less development time): 11 uniques (vets included: Snake, Pichu, Squirtle, Ivysaur, Young Link, Wolf) and 4 clones so that would be about 12 slots. Eish... Looks like we could have 3 uniques left (or 2 and 4 echoes).
On the flipside, they aren't making this game for both the 3DS and Wii U, just the Switch. Also, it appears they aren't doing custom moves this time (thank God). Also, the estimations can get pretty wonky on how much they actually have to dedicate to development since six veterans (and four echoes) would be, theoretically, quicker to make. It could be that they could squeeze one or two more unique fighters (or one and four echoes) in and in that case, I think Shantae would be next up in line. However, she would need those previous two points in her favor (being the indie rep and having Sakurai fall in love with her potential) in order to beat out the remaining competitors.
It looks like a tough fight but who really knows? We also have potential curveballs to deal with and "Sakurai bias". Even though it looks (kinda) bad, I do still feel pretty optimistic though. Namely because I think those two points I mentioned WILL be in her favor and she WILL get squeezed in. At this point though, I think she'll be the very last reveal though. It also helps her that she fits the mold of a (current) Nintendo marketing strategy (promoting indies). Money talks.
Hopefully the remaining ballot contenders get in through DLC and don't just get shafted because they didn't make the base. On the flipside (again) I could be completely full of **** and Sakurai is going to add in a Space Invader next.