There really isn't a good explanation for any of this huh.
I wouldn't be surprised if it's nothing, or just some weird internal thing, but at the same time... what if it isn't?
We could absolutely get a random "new content approaching" video and a minor update like small battlefield. Especially if we really do have to wait ages for the last fighter, and this update would give us some minor content while we wait so it doesn't feel as long.
If it is a minor update, I'm going all in on an octoling echo. It makes too much sense in this scenario to not be a thing.
Also, this is absolutely not a copyright thing, since that doesn't make any sense, at least to me. The only time copyright affected a Smash presentation was the Hero one, when they couldn't use DQ music outside of the demonstration match. It wasn't even used in the mii costume stuff. And, no matter how much people hate Konami, I really don't see them being Sugiyama levels of stingy.
No matter what it is though, I doubt we're getting the final character in it. Honestly, if this does end up being something, I feel like we're going to be waiting a while.
Also, my absolute dream scenario would be them adding additional music to each series, including dlc. Not having Persona 2 music is a crime.