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?
Atlus: Don't really see it. I'm very much aware that Joker doesn't rep SMT at all, but considering he came in just last season, I think they might go for something else. Especially considering Atlus is a part of Sega and they have other stuff to offer.
Sega: It's possible. My bets would be on the two you mentioned, with Axel Stone and Alex Kidd as dark horses (I think their new releases came too late to be taken into account, but you never know).
Konami: Really don't see it. With Bomberman as an AT and Goemon as a Mii, that leaves... Frogger, who I don't think is DLC material despite being personally fond of the idea - or a Silent Hill character, which I don't see happening if RE couldn't make it despite being easier to tone down and being more action-oriented.
Capcom: Dante and Phoenix are the would-be frontrunners, but Amaterasu shouldn't be taken out of the running just yet. For MH... eh, considering they barely appear in Capcom's own crossovers and that Rathalos was base game content, I'm not really counting on them, even if they're still possible.
Namco: Pretty much the ones you mentioned. It's gonna be really weird if Namco ends Ultimate with only one guest considering they're literally helping with its development. But I guess weirder things have happened in Smash...
Square: Hard to say. 2B is a character I can see Nintendo/Sakurai going for and being pushed by Square, but Sakurai only met with Yoko Taro after the Pass was decided. Geno is pretty much backed up by popularity. Lara is a western character inside Square and wasn't developed in-house (a similar situation to Kunio in Arcsys, minus the western part), which could affect a potential push for her. The rest... I'm not sure if they're high profile enough. Time will tell.
Microsoft: Not only does it have two high-profile picks, they're frontrunners when it comes to western character. Very good position for a double dip.
SNK: Based on what Terry came with, I doubt it. Maybe next game.
Tecmo: Haybusa would be their frontrunner, I guess. I could see Warriors, but DoA... nah.
Arcsys: At this point, I think they have a shot. Hard to say who has the lead between Ragna and Sol, but I think either of them could happen.
Ubisoft: Don't think so... their biggest series are either Spirits or Mii Costumes. And sadly, Rayman lacks the clout in Japan.
Activision Blizzard: Crash is a general western frontrunner, nuff' said. From the Blizz side... hard to say. OW and Diablo have the Nintendo connection, but I'd argue WoW and Starcraft are more significant in the long-term.
Falcom: Probably Adol. He seems to be the closest to a "company mascot" here. From Trails, I
want to say Estelle, but Rean would probably have priority due to being more recent and his games arguably being more popular.
BONUS
Riot: May or may not happen, but I think people are sleeping on the possibility
really hard, especially with how close Nintendo has become with their owners in the past two years. It's a bit hard to say who would make it, but my bets would be on Ahri or Lux.
Nippon Ichi: ...Someone from Disgaea? Kinda doubt it, but hey, it's possible.
Indies: At this point, probably Reimu or Quote. Pretty much the two Indies I can see having the best shot due to their history and, in Reimu's case, japanese popularity.