Would be way more interesting if they would really start when enough people tune in but chat before that and maybe share some tips and tricks.
Great combo with a sale or updates, greater combo with being influenced by the above.
"We'd also like to remind you of ARMS. There's no update or anything, but I asked Stan, who tuned in first, which old title we should highlight and he picked ARMS."
I can see, basically, two options. Option one is that DLC isn't taking all of Sakurai's work time, so the "next" project is actually concurrent with Fighters Passes, in which case we definitely could see it on the Switch, unless it's huge. Option two is that DLC is taking all of his time; in this case, it's impossible unless Switch gets, like, DS tier lifetime, and the next project is probably the "reconceptualized Smash".
In case of option one, it's generally hard to predict Sakurai given his supposed dislike of sequels, but I would guess he would want to tackle a genre which he didn't really mess with before too much. So not a fighting game, not a platformer, not an arcade puzzler, not a rail shooter or TPS or FPS (since it's close to TPS). Did he ever make an outright RPG? I'm afraid he could go for an RPG.