Knight Dude
Keeping it going.
This is about to be a long post. Hopefully you guys don't mind, since it's not like there's much in the rumor mill, something I'm more than okay with at the moment, if I'm being honest.
Sure. None of the added characters were spirits beforehand. So that's the most reasonable conclusion to jump to. One that I even agree with. The only reason I don't see it as outright impossible is to compare it the DLC in the Previous game. Trophies, the equivalent of Spirits(though who you ask, one might have more importance over the other) in Smash 4. We had trophies of Lucas and Mewtwo respectively(in both versions no less), as they were Non-Playable characters. Then, those two, among others were added to Smash 4's DLC roster.
For the Fighter's Pass, each character was likely already chosen a while back, probably near the same time as the base was completed, if I had to guess (unless stated otherwise). Because of this, each one would have to stand out on their own drastically, and I'm sure plenty of us could make an argument as to how a popular character from an already present franchise in Smash could still accomplish this, I believe many could. But no matter who they were, they couldn't exactly be the same as bringing in a whole new franchise to, like Fatal Fury or Banjo-Kazooie. These series also needed to bring in their own spirits. Which again, some present series would have a very easy time doing so, others...not so much.
For the post Fighter's Pass/Fighter's Pass 2 DLC or whatever it'll be, we don't know the exact process of who'll get picked and why, not that we ever truly did outside of a few notable characters, but you get my point. I would like to think that the characters chosen could be a Spirit already and it not matter too much. Because at the end of the day, many of them are just PNGs. Some are also assist trophies, but since they serve a more direct role in the game's standard means of play, it would be harder to justify giving them a fully playable role as well. If they did, I'd honestly bet on Waluigi, cause the dude's been asked for the most.
There's also characters who show up in someone else's Final Smash, Chrom, albeit as an echo of Roy with Ike's Up-B. I'm unsure if Shulk could even get an Echo Fighter, as the only one who could potentially fight like him is Dunban, who specifically can't use the Monado to it's Full Power like Shulk(though he's the only one badass enough other than Shulk to use it at all.) And in Mega Man's case, Protoman and Bass could act as his Echo fighters.
If we're talking fully unique characters from a Final Smash being fully playable, this clearly opens the door to Fiora, Dunban being made properly and all the other Mega Men. Riki's already an assist, so maybe he'll be the first to pull off all three somehow.
