I still believe base game content doesn't affect anything anymore, since these characters weren't planned to be in Smash at all. Originally it was just Volume 1, that would've been the end. (Oh god, Byleth then...).
However, post launch content is something much more worrying. It's possible that Spirits are being used as a "sorry, I failed to negotiate for them" button. Which would be pretty bad news.
I can understand why people would believe that Spirits are permanently out, but it just has that feeling of being either based on Byleth, who was planned from day 1 (of DLC, I'd be very surprised if protagonist from Fire Emblem NX made the original cut for the roster but at the same time very unsurprised) and people's emotional reactions to them, or simply assuming more of the same.
But if Spirits are out, and fully out, then are they going to do 6 third party characters, with what seems to be a budget that's not very viable? Somehow I doubt that. Every relevant first party character is in as at least a Spirit, if not an Assist, Cameo or Boss Fight. I dunno, it just doesn't seem very financially viable to attempt to do this, with how profits are going everywhere...
Unless, the pass was as unrealistically fan hype as possible. Like, 6 characters with worldwide, global appeal that get people talking. And, I dunno if there are enough third party characters, purely relating to video games, that could pull that off. Maybe 3 or 4, but at some point you're gonna have to get regional. And those won't be big sellers.