Spirits have been very much advertised as a replacement for trophies, if with more gameplay function, like the stickers tried to have. With that in mind, I sincerely doubt that being a spirit is a deconfirmation, even when they have a small part in World of Light, as a shop keeper, trainer or so on.
Sure, the playable cast only has alternate versions of themselves as spirits, while the regular versions are Fighter Spirits, but a very similar thing happened in For, where people thought Mewtwo and Lucas were deconfirmed since they had regular trophies, only for them to become DLC in the end, complete with new trophies.
Besides, we have stuff like Karts without any racers as spirits, meaning that lifeless objects are being treated the same way as actual characters like Mona, Toad or Impa, I sincerely doubt that Sakurai and his team take the spirit premise serious enough to make it an argument to deny characters a spot on the roster.