What even entails in a Smash reboot? A reboot implies we need a timeline fix because Smash 4 retconned the series after Tabuu killed Master Hand in Brawl, or that the current platform fighter formula needs to be absolutely replaced with something else entirely. This isn't like Mortal Kombat where you ****ed up the story so many times you have to do a full reboot trilogy to fix your mess from 9 - 11, or like Street Fighter where you need to sprinkle prequels and sequels in a timeline to justify making more games. Smash doesn't have such a thing, and any Story Mode has no true impact on the series itself because its a celebration of gaming, not the longest-running story of fanfiction.net, which is a SSE fanfiction probably.
Gameplay changes? Moveset changes? Roster changes? That happens every game.
There have never been any complaints against starting 'anew'; doing new ideas is the company's motto. Each Smash game is always doing something different; not through core gameplay, but experimenting through other modes. But the process of redoing Smash entirely poses the question of what that even means. And no one's really clarified outside of the roster or movesets just being less than this current game's.
The topic was the roster, the tweet just implies a reboot only involves doing a complete roster change. But what does that even mean? You'd just be adding and subtracting like normal. I just believe we'll have the ability to have all of the Smash characters from Ultimate in the next game.
If Smash really was to go for a "reboot", as many are suggesting, one would have to wonder: how would you even overhaul it in a way that completely separates it from the entire franchise as it exists now? And especially in a way that would warrant curbing the roster to any significant degree? Health bars? That's what stamina battles are for. Team-switching? Is it really something that couldn't be done on the current engine (besides which, Smash stood out to begin with for being one of the only fighting games to allow simultaneous team matches)?
I think I have some idea of what you mean, though I wouldn't mind hearing some specific examples.
There are lots of ideas for the reboot.
-Having a bit of genre-changing. 3D Smash Bros similar to Power-Stone and/or Arms would be a cool addition to Smash 6. Going full 3D would be the next evolution of smash
-Maybe Action RPG similar to Kingdom Hearts where you explore different gaming worlds.
-A 3D Battle Royale like Fortnite but with different abilities for different characters. I mean Smash Bros is technically already a battle royale and it's one of the first ones. Why not go all the way. Maybe that way Everyone is Here can be possible.
-F2P like Multiversus.
Maybe not a genre changing but a change of theme.
-A return of form to a Nintendo All-Stars.
-Smash Bros vs Shonen Jump
-Maybe Assist Trophies Smash where only the previous assist trophies are play.
Even that, Smash 6 doesn't even have to be game. A Smash movie on the big screen would be cool to see.
-With Video Game Movies becoming good and now popular such as Sonic Movie, Monster Hunter and Detective Pikachu with upcoming ones such as Mario, Minecraft and Mega Man coming in the future.
-This would be a great time for Nintendo and Sakurai to capitalise on that can bring 'em all together in one big Smash Movie. There is a reason why MCU is such a huge cultural hit amongst with anticipated hype for NWH and a reason how Endgame became the 2nd most grossing movie of all time. This could be Nintendo's chance to use their formula to reach similar heights. A Smash Cinematic Universe if you will.
There is still so many ways of what Smash 6 could be as eventual reboot. It doesn't always have to be an Ultimate 2.0. EIH isn't sustainable anymore. Cuts and changes are going to happens. Every franchises especially fighting games goes through with it regardless of reception or demand. Smash was no different with Brawl and 4 and it will happen for 6. It's unfortunate but it is what it is.
But as I explicitly pointed out with the points above, There still ways for Smash still be successful, eventful and still feel big, if not even not moreso, as the reboot if Nintendo and Sakurai play their cards right.