So does anyone remember that article that demonstrated how it would've been more difficult to fake the Grinch leak than to have it be the real deal?
https://www.videogameaccountant.com/2018/10/29/grinch-leak/
With the Rare Spirits we have precedence that the development team are sometimes ahead of themselves when it comes to conceptualizing what could be the game, before actually sealing the deal and ensuring its inclusion. Consider also that the Chorus Kids were found in 4's data, that Isaac did in fact return as a super-detailed AT, and that whole business about Sakurai needing some Mach Rider looking figure for the visual basis of what he was working on at the time.
Because there's no surplus evidence to stop me, I'm appealing to ignorance and going to say that the Grinch Leak was simply an extremely early "final" rendition of the banner, subject to cuts and additions in the time between its inception and the beginning of Ultimate's promotional roll-out. Said characters who never manifested in the final roster could be subject to a vicious rotation of insufficient priority, development issues, or were just unable to comply with the structure of chronological marketing that would most kindly benefit the interests for all parties involved with Ultimate. Keeping what remains of their code inside the proverbial 'toybox' is a great way of holding on to easy opportunities to milk future DLC. Because with no sequel to Ultimate in sight, and millions of people always open to more content, how could you turn down such a bonafide method of profit?
Couple that with this story of sighting plans for a Banjo Amiibo (although could that not have just been the Tokatu figure that released this year?), or the theory of Plant's Amiibo being out so early because it was supposed to be part of the base roster before a still-developing character compromised plans.
It's true, a Battletoads/Killer Instinct/Minecraft character could purposefully serve as a mediator between Nintendo, Microsoft, and the fans' wishes, but only one has been championed by the company's head twice on two separate occasions, over multiple years and multiple games. In keeping with this theme, you would definitely not want B-K as a character out before:
- The Nintendo 64 Classic
- The formal announcement of Xbox Live on Switch, and what that entails
- The lead up to the release dates for either of those things
One simple Direct could set fire to all of this, but I still have faith.