I don't think there's anyone who I could say is 100% disconfirmed post-Fighter Pass, but DLC Spirits come closest. I'm sorry, but I think these characters wouldn't have been added as Spirits if Sakurai had bigger plans for them. He probably would've saved their Spirit for when they became a character.
Next would be DLC Mii Fighter costumes, which I don't think are as telling as DLC Spirits, but still pretty bad for a character's chances. Why make the costume if they're gonna be playable anyway?
Next in line are ATs, which I'm not really sure where I stand on. It's possible Sakurai could add them since the second wave wasn't planned before launch, but then again, they have pretty significant roles already. It hasn't happened before, which makes it a lot harder to say it's still possible without being influenced by a bias.
After that, I think everything else is fair game. Stage cameos and base game Spirits should be fine.