What will Nintendo do with the next Smash Bros??
This intrigues me to no end.
They literally did the 'Ultimate' version of what Smash has been building toward since Melee. What now?
It is hard to imagine just another typical Smash. I would probably not even bother with it and just keep playing Ultimate on the next-gen (assuming backwards compatibility because Nintendo execs would need to be locked up in a mental hospital if they didn't do backwards compatibility).
But Smash is so popular it is also dangerous to mess with the formula.
The only thing I can think of is to just make it a free game on NSO Expansion Pack and just keep building on it over time, to entice more people to get NSO. Putting their ultimate competitive online game on their online service to push sales of that service to be a more premier service definitely makes sense if they want to start taking online seriously. Then they could keep the same old formula because it'd no longer be a new Smash that needs to try to outdo the last one, because it'd be 'Smash Online'. It'd be like a recognition of having made the ultimate version of the game so they won't try to one-up that but instead just build out a final free (with the subscription) online version for which content is continually added over time.
With that online version of the Smash we all know and love always there to play, that might even free them up later on like say the following generation, to start a new epoch in Smash and experiment with a new formula for the series since the tried and true Smash would still be available with the online service.
Other than that I really can't think of what they could possibly do to grow the series from literally the 'Ultimate' version. Iterating on the same formula feels like a very 'meh' idea at this point. And totally changing up the formula risks making a misstep and losing the huge audience on one of Nintendo's premier series.