(Two of the pics not working without quotes, bear with me)
(Tried uploading them from Discord; if you can't see them, my apologies)
Ladies and Gentlemen, I bring you a new theory.
Title Screen Theory.
But rather than be a theory of who could show up, it's a theory mainly of who
won't show up.
And that is, ANY character that would require another copyright credit.
Observe, the title screen.
It covers the
entire screen.
"But Golden-sama, what about the blank space after Hal Laboratory? Surely credits from the row below could be moved up there to make room after Square Enix, right?"
Technically, it
could, however it is VERY unlikely.
Why, you may ask?
Because that gap is there for by intentional
design choice. A design choice that was present in Smash 4's title screen as well.
Before DLC:
After DLC (Couldn't get one of the English screen for some reason):
Ergo, characters like Steve, Banjo-Kazooie, Sora, Shantae, Isaac, etc.?
Not going to happen.
.....at least in base game. DLC could shake things up somehow, who knows.