Release date: December 7th, 2018
According to Sakurai, we shouldn't expect too many new characters and we will know all characters before release. Until proven false, I'm taking that to mean we're not receiving more newcomers than the previous Smash installment. In other words, no more than 17 new characters (I think that was the most added?)
We know of 9 already:
4 Echoes (Chrom, Richter, Dark Samus, Daisy)
5 Newcomers (King K. Rool, Ridley, Inklings, Simon, Isabelle)
So that means we've got around 9 or less characters less to reveal (unless Im wrong about that 17; in which case we could have a few more)
It's likely to be roughly half & half (meaning half uniques and half Echoes)
There's only 2 months (October and November) of reveals left unless they do a final trailer during that last week of December before release and show 1 'surprise' character
As much as some people may hate it, Vergeben has yet to be wrong with his sources, which means it may be safe to assume that we've got these still:
1) A Square Enix Rep
2) A Pokemon Rep (1 source of his confirmed as Incineroar)
3) Ken (most likely as a Ryu echo, but who knows at this point thanks to Isabelle)
So, assuming those to be real, we've got roughly 6 (out of 9 unknown) characters left + an explanation of 'Spirits' mode for the game.
What's the likely course this will play out in terms of reveals then?
My thought would be this:
October: Smash focused Mini-Direct- 3 characters (one Unique; 2 Echo) revealed, Online play detailed
November: Smash Direct- 5 newcomers revealed (3 Echoes, 2 Uniques), More detail on gameplay; such as 'Spirits' mode, another unmentioned mode, more talk of online, Sakurai talking about development of the game over the last X years, talk about role of the Ballot in choice of characters, which characters were close; etc; close out with talk about future DLC (or possibility of)
December: Final trailer for game shown off; ends with reveal of final newcomer
That would be my guess as to how the rest of this plays out, anyway. I really wish the Square rep would be anyone but Geno, but he's the likely choice (unless the port of TWEWY put Neku at the forefront). And f not Skull Kid, I really would like to see another unique Zelda newcomer as its Nintendo's 3rd largest & most popular franchise, but so far 50% of their representation is Link in one way or another. (Seriously, 3 Links & Zelda, Shiek, Ganon). I would have liked a combo Midna & Wolf Link, but since that Midna has been seen as an AT, I'd be better off rooting for her 'True' form to be in (though that's unlikely). That leaves just Skull Kid (memorable Zelda villain not named 'Ganon') or one of the Heroes from Breath of the Wild due to its wild success. What do I fear will happen? Linkle....a 4th Link.
Pokemon is likely Incineroar as its the most promoted, looks the most awesome if Sakurai was going off of pure design & concept art (not to mention Ash was in Incineroar's concept art, so Sakurai would know who Gamefreak would be 'pushing' so to speak), and Decidueye is already in Pokken (and I'm not sure Sakurai wants to double-dip with his fighter choices. Tapu Koko, Necrozma or another Ultra Beast also have a chance due to being story-centric and very pushed in marketing (especially in the 'Ultra' versions where Ultra Necrozma was essentially a 'boss' encounter and a major part of the story).
As for Ken....he's likely an Echo, but that's also what we thought of Isabelle who turned out to be a semi-clone. And that brings me to my next topic. I think this kind of helps clarify Echoes for us. Isabelle is unique instead of a clone because she's got several moves that had to be created from the ground up instead of just palette swapped like Richter's or Dark Samus. She's got a Fishing Rod special, instead of a Tree, she buries the rocket in the ground which fires up, multiple attacks that are completely different (like the cheering pom poms), and a Final Smash that is similar to, but not exactly the same as, Villager's.
Compare that to Richter, Chrom, Daisy, and Dark Samus who:
All share the same frame as their 'Echo'
All have the same attacks; just color-swapped
Vary only in subtle ways like idle animation, speed, or 'floatiness'
Chrom has a different Up special than Roy, however it's the same as Ike's (only he goes with his Sword instead of tossing it). It could be argued that he differs a bit more than other Echoes because he was already in Smash 4 before being cut, so this may have been the moveset they had programmed for him before he was traded in favor of Robin. The data variation for him was likely already present, so they added him as an 'Echo' this time.
Basically, what I'm saying is, Echoes are just 'skin' variations that change out the 'look' and some attack aesthetics (with possibly Taunts or an idle animation looking slightly different). Once you start to program more and more to differentiate them, then they're no longer Echoes, they're unique characters. Not to mention, even though it hasn't been explicitly stated yet, but all Echoes thus far are based on characters within their series: Peach/Daisy (Mario), Samus/Dark Samus (Metroid), Simon/Richter (Castlevania), and Roy/Chrom (Fire Emblem). Which is also why we have the ability to 'combine' them on the character select screen. Everyone's grouped by series, so you're not going to have, say, Blaziken as a Captain Falcon echo. It's not going to happen; sorry. And for those who would try and bring up Ganondorf? He's changed enough so that he's no longer an echo; I believe the concrete proof to that would be in the fact that he's his own distinct number; no 'e' in sight.
This would pretty much be my argument against Shadow making it in as an Echo as well. He differs too much from Sonic to be considered an Echo. If he's in, he gets in as a Unique character. If Sonic does get an echo, it'll be Metal Sonic as the only difference for him is purely Aesthetic; he's literally just an evil, robotic Sonic. Shadow doesn't even run; he skates; plus he uses 'Chaos' powers. He'll have a Spin Dash, but that's it (if he's in).