Characters with no games on the Ness, Super Ness, N69, Gamebox, We, We Two, Switcharooni, Game and Game, Game Kid, Game rainbow, Game Advanced, Dsus, 4DS, or the virtual dimension boy
Chance: 10%
Of course the idea that a character must have Nintendo presence is a fan rule. And Sakurai himself stated that it is a courtesy for a character to be on a Nintendo system, not a requirement. But so far this rule has held up strongly and is one of the few fan rules that I believe in. But the reason it is holding up well might have to do with the characters simply not being a priority and/or having other obstacles. Let's break this down.
Master Chief: Suffers from the "One character per third party company in each pass" rule which, unlike other fan rules, has some evidence to back it up. Mostly the fact that Steve was in negotiations for years, plus there are theories out there suggesting that Sephiroth may have been negotiated for around the same time as Hero, and yet they were put in different passes from Hero and Banjo. Admittedly you can say that it would be stupid for Nintendo to limit themselves and Master Chief would be the kind of character to break this barrier, but with only 3 characters left and very little room for major third parties, I don't think he is happening. And I say this as someone who really wants Chief.
Monokuma: Danganronpa's popularity has died down a bit and the future of the series is uncertain. It is also more on the niche side, not obscure by any means, but the fact that it isn't on a Nintendo system really hurts it because it doesn't have the same level of popularity as series like Halo or Half Life which can sell itself better by just its name recognition alone. I know being iconic isn't the end all, be all, as the man himself stated. But if Nintendo isn't able to directly profit from it, then they would probably at least want the character to be very recognizable or have a very large amount of fan requests.
Sony characters: Not happening in my eyes. Sure Kratos is in Fortnite so in theory they might play ball. But that doesn't make up for the fact that Nintendo and Sony haven't had any collaborations at all, at least to my knowledge (Well, aside from the collaboration that ended abruptly and resulted in the creation of the PlayStation). There are just so many companies that are much closer to Nintendo that them going to Sony for a character would be the biggest curve ball in Smash history.
Valve characters: You could make an argument for this. In Japan
PC gaming has been growing, Steam is huge in the West, Sakurai himself
praised Half life, and Gabe Newell has stated
he would be fine with Gordon being in Smash. With that said, Nintendo and Valve don't have much of a connection so it's hard to see Nintendo approaching them, despite them having some very high-profile series like Half Life, Team Fortress, and Portal.
2B: She also suffers from the same rule that hurts Master Chief, and is also hurt by her series being more niche. Plus Sakurai met Yoko Taro after this fighters pass was decided, which is a death blow.
World of Warcraft: It's a possibility. I did just argue for PC gaming in Japan and WoW is big in the West. But the fact that it's owned by Activision, who also owns Crash and Overwatch, is a big obstacle. Heck, Diablo 3 is on the Switch and Spyro got a revival too, so they are factors as well.
Overall, yeah it's not looking good for any of these options. I think the fact that they all are not on Nintendo hurts and when you combine that with everything I've mentioned, I don't think any of them are strong contenders. With that said, anything is possible and I have a feeling one of these characters might happen since they are all good candidates for the game.
Want: Abstain
Look. Don't get me wrong, any of these characters would be great. Master Chief, Monokuma, and Kratos are some of my top most wanted and I would be very happy with 2B and any of Sony's series like Uncharted and Ratchet and Clank as well as Valve's offerings which are juggernaut series. But I have to abstain from a want score as we could get WoW which I am less enthusiastic about and there is the slim chance we could get something else that I'm not thinking of. Otherwise, I would definitely have given this a high score.
Prediction: Qbby: 9%
Noms: Excitebiker x10