A few things I think should be considered:
1) Since that Famitsu column where Sakurai pointed out the struggles of making distanced development for Smash, where he mentioned "working with publishers". Awhile back, I went over the difference between publisher and developer, and how the term itself has meaning within the context. There were a few important sentences.
A few things to note...Nintendo is mentioned separately from "publishers". Developers like Intelligent Systems or GameFreak are not considered publishers, but larger companies like Namco, Capcom, or Square Enix are (think of the meeting for Hero). There are plenty of publishers, so this isn't specifically those 3 companies, but it should be noted that, at the very least, we're looking at at least 2 publishers that aren't Nintendo, ergo, there's likely at least 2 3rd parties. I would say it's more likely that it's 50/50 3:3, though I don't have anything to base that on. It's a feeling I have, and that's subject to change in either direction if assist trophy/mii costumes are on the table for "upgrades" or legitimately off the table.
2) I think that it's highly likely that a new company will be included in Smash by the time we get Challenger Pack 11. This doesn't really narrow anything down, but I think, if it's a Japanese gaming company, companies like Koei Tecmo or ArcSystemWorks are in the mix. However, I would also argue that any company with a playable character in that isn't from SNK is on the table as well. It seems reasonable to me to expect AT LEAST one character from a new company, and AT LEAST one character from a company already collaborating.
Atlus seems to be SMT3/5 or bust. SNK is most likely out given the wide berth the Terry pack covered. Namco has Pac-Man and Tekken covered, with Tales unaccounted for. To my knowledge, there appears to be a drop off of popularity after that, thought that doesn't disconfirm Namco by any means. Capcom and Square Enix both have substantial backlogs with untapped potential, so I wouldn't be surprised to get a character from either company (though I doubt more than one from any given company, aside from Nintendo for obvious reasons).
3) Each "Season" of Smash DLC has included at least ONE "marketing" pick as defined by the fanbase. Corrin was first, Byleth 2nd, and now Volume 2 has started with Min Min who seems further away from a "marketing" pick from the previous two, though she could arguably still be considered one. Therefore, it's possible that we could still get a "marketing" pick from Nintendo, which I could see being from Pokemon. I have to agree that games that are still unannounced may not be in a great spot to get a playable character at this point, though it's tough to say that for sure.
Characters I could see from each company, to make things more concrete:
Atlus: SMTV protagonist, Demi-fiend
SEGA- Kiryu, Arle
Capcom- Dante, Amaterasu, Monster Hunter, Phoenix Wright
Namco- Lloyd Irving/Yuri Lowell, Soul Calibur, Dark Souls
Square Enix- 2B, Bravely Default, Neku Sakuraba, Geno, Lara Croft. A lot to go around here
Microsoft- Master Chief, Steve Minecraft
SNK- oof
Koei Tecmo- Ryu Hayabusa seems like their Terry, though I guess I can't rule out others
ArcSystemWorks- S(c)ol Badguy, Ragna the Bloodedgelord
Ubisoft- highly questionable based on content they already have, but Rayman probably. One would think Assassin's Creed and Rabbids costumes would come with Rayman, no?
Activision- Crash Bandicoot
Falcom- Trails in the Sky (funny acronym lmao amirite), Ys to name a few series
What do you think?
I'm gonna go ahead here and address my thoughts on each character you listed. I don't have a super great understanding on all of them, but I'll try my best, lol:
Atlus: To be quite honest, I'm really doubtful of more Atlus content. Persona and Shin Megami are radically different games, but TBH I still feel even with that in mind, Joker and Persona already being in may be all Atlus and Nintendo really wanna go for. I fully understand this is shaky reasoning, but I'm just not sure I see SMT being a high contender, especially when an Atlus rep will be contending with other Sega reps due to being a Sega subsidiary.
SEGA: Sega is interesting to me here because I feel there's a decent amount of untapped potential here depending on how the rest of this DLC turns out. Kiryu is a wild card that I'm not sure how to feel about: He feels like a darkhorse pick that would make a ton of sense in hindsight when you look at Sega's marketing ATM, but I'm not so sure he has enough of a leg up on Arle. Puyo Puyo is incredibly popular in Japan with a growing userbase over here in the west that Sega is continually trying to grow, and it has the benefit of appealing to a wider audience to boot. I feel if Sega is getting a fighter, Arle has the edge here.
Capcom: Dante. In my mind, it's almost assuredly Dante if Capcom gets another: DMC is being pushed very heavily by Capcom ATM and there's the benefit of having the requests for him acknowledged before pass 2 would've been in the planning phases and ports of his games were on the way to Switch, bolstering his popularity amongst Smash fans even more. I'm not a Dante fan at all personally, but in my humble opinion, he is the likeliest character out of anything suggested right now given how both Capcom and Nintendo seem to have an interest in DMC content right now. Phoenix Wright is a dream character for me, but looking at Capcom right now...DMC is clearly the higher priority for them.
Namco: My heart wants to say Yuri, but my I know it's probably going to be Lloyd or a Soul Calibur rep. Dark Souls could happen as well.
Sqaure Enix: I think the prime suspects are 2B and Bravely Default. 2B fits the same molds that Joker does, while Bravely fits the ones Dragon Quest did. Sora is a no 'cause of the Mouse, Neku is a sleeper pick I could see happening, I personally don't think Geno has incredibly great odds due to competition and treatment from his parent company, and Lara is a huge potential that I'm floored no one talks about.
Microsoft: Microsoft is tricky: I'm personally not convinced another character is in the bag as much as others do. Master Chief I think is a huge pipedream addition IMO, and Steve feels like he's in a weird spot due to complications communicating with western developers. If either one is coming, though, my money is on Steve: Minecraft has a huge presence on...everything, and the Nintendo audience is exactly the kind of audience you'd want to cater content for it to.
SNK: They're done.
Koei Tecmo: They're in the same position Platinum Games was in during Smash 4's DLC: Extremely chummy with Nintendo and have a wealth of characters that would appeal to Nintendo's home market of Japan. Ryu makes a lot of sense, but I think Atelier could be a sleeper pick as well with that series starting to grow and get a lot of focus from KT. Hard to tell ATM.
ArcSystemWorks: Don't know enough about them to comment, honestly. Their games ain't really my scene.
Ubisoft: I think they're out like Bethesda. The timing of the Mii costumes don't make any of their picks look great, especially the Rabbids not coming with Rayman.
Activision: Crash or nothing. Spyro would be
amazing, but Crash is the choice no question, and I'm fine with that. This one is probably the most likely western pick if we got another one coming.
Falcom: Ys is a pick that would make a ton of sense in hindsight, not sure if I see Trails in the Sky.
Those are my thoughts. Not the best takes probably, but this is how I'm viewing things ATM.