I'm not saying it's definitive or anything, and I'm hearing about it second hand, just that it's what some circles are talking about. I guess someone contacted PapaGeno about it? Hopefully
this works. PapaGeno has never struck me as a guy who just make something up for the sake of it, and he's rarely this vague.
Also, to be faiiiiiir Assist Trophies have never been upgraded before, but we're all hoping for that! So it's not like them doing something unheard of for the anniversary of their parent company's mascot's franchise is out of the realm of possibility. Maybe they were meant for release on the anniversary, rather than being revealed on it, but Covid got in the way?
I just don't think saying "Well, Min Min didn't get revealed or released for ARM's anniversary" is relevent when you can't argue ARMS is in the same league for Nintendo as Mario's 35th anniversary might be. Nor how big of an impact a hugely desired character like Geno or Waluigi might be.