I just thought of something very interesting to speculate about ...kind of off topic from what everyone else is talking about but anyways, what if Sakurai adds Nightmare from Soul Caliber as a odd curve ball and he plays a major role in whatever the spirits mode may be. I’m not saying his inclusion is likely but the only reason i would see him getting in is Nintendo’s clever way of paying respect for what Soul Caliber ii did with Link. Imagine him teaming up with Taboo, Ganon, Ridley, Mewtwo, skull kid (assuming he’s in), and all the other villains.
Another interesting character I saw in one leak, can’t remember which one it was but it said Tekken gets represented through Heihachi...if this is true then smash would have almost every major 3rd party fighting game.
Last thing...when looking on villains wikia I found this Nightmare bio about its personality to be very interesting: “In the games, Nightmare has been portrayed as a violent, ruthless, emotionless, aggressive, and detrimental misanthrope, constantly in search of souls to restore Soul Edge”
That had me thinking...if they included Nightmare he would fit perfectly into the spirits mode if it has some type of plot line. What if Nightmare has all the villains/bosses as his henchmen sent to retrieve the spirits/souls of the heroes for him. I think it would be really cool to see an adventure mode where you have some type of hero and villain version of the mode (well that’s to say if spirits mode has any type of story line at all which doesn’t seem too unlikely imo).