Sakurai has recently said that he doesn't have plans for the next Smash right now, and that he can't imagine Smash without him.
Masahiro Sakurai: 'I Can't Imagine a Smash Bros. Title Without Me' (vgchartz.com)
If Sakurai is telling the truth about the preproduction of the next Super Smash Bros. and he is going to lead it again, we're looking at no new Super Smash Bros. until at least Q4 2025. The reassuring part of the wait is that Smash games have always taken under 3 years to make.
Super Smash Bros. is turning 25 in 2024. I think there's a way for Nintendo to make some easy money on celebrating Super Smash Bros.
-Super Smash Bros. on Switch Online: There's no reason for this game not to be with the N64 games.
-Super Smash Bros. Melee HD: Keep the gameplay the same, remaking graphics is optional.
-The Subspace Emissary HD: Either port The Subspace Emissary or remake it with the gameplay in Ultimate.
-Smash Run HD: Remaster the graphics from 3DS or outright remake Smash Run with the gameplay in Ultimate.
-Super Smash Bros. Ultimate DX: Nintendo could release this game in 2024 if Switch 2 launches, then, or it could come out in 2025 after the 25th anniversary is over. It's pretty obvious what you can do with an enhanced port of Ultimate: all DLC, another fighter pass or two, improved online, improved performance maybe the return of trophies or at least adding trophy bios to Spirits.
If this comes to pass, Nintendo could probably skip the next Super Smash Bros. on Switch 2 and we could get a sequel to Ultimate in 2030-2033 on Switch 3.
Lifetime Sales Predictions
Switch: 151 million (was 73, then 96, then 113 million, then 125 million, then 144 million)
PS5: 115 million (was 105 million) Xbox Series S/X: 67 million (was 60 million)
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima