Now that the dust has settled a little bit, I think it's time we take a step back and look at the bigger picture. Specifically, the Mario-focused Smash event. As far as I'm aware, they've never announced events like this where it's announced a month ahead of time. Considering it's being held from November to December, and events like this have only lasted a few days at most, that also makes things suspicious. Another thing to point out is in September of last year we already had a Mario-themed event, with characters, items, and stages from the series being the focus.
With all of this in mind, another Mario character may be coming to Smash before then, probably revealed and released in a Mr. Sakurai Presents video. It'd make sense given this event is Mario themed and since Hero they've always had events based on the character after they're released. Something else to consider is that with each passing day, the closer the December 2021 deadline comes. It's a matter of how long Nintendo can hold the proverbial bladder until more Smash news is announced.
But who knows, I could be wrong and this could just be a standard tourney event they spontaneously decided should be announced ahead of time since they needed to pad the direct.