It could be the last Smash game to feature Sonic though, who knows.
For now, I regard it the last Smash Bros. game. I think that SSBU is supposed to be the penultimate and finale of the series, that Masahiro Sakurai made it to superb that he cannot further improve on its perfection... However, fans and probably Nintendo themselves are bugging him for more sequels, and he probably doesn't want to because to him "how can you improve perfection?"
The only way I can see it for him, if he can't continue the series, then expand it with spin-offs. Smash Bros. games that are sub-par to Ultimate or SSB4 but have their own gimmick or tide the fans over.
From what I understand, Persona series consist of five games and a butt-tonne of spin-offs so he could go down that route if he wanted.
In Japan the VF3tb community is still alive and there's yearly fan tournament of it.
SEGA is just responding their enthusiasm, that's why this arcade game is exclusive to Japan only for now.
Oh that makes sense. I mean, it's not milking if it had steady and on-going interest.
But even SEGA never said that.
What SEGA said was "Genesis does what Nintendon't" ... so I'm gonna say "Genesis does what Nintendon't"

I know, I usually refer to it with Sega in general... but I guess you're right in this cage given it's about a game for SNES and Genesis.
Plus, I called it the Mega Drive, and I only had 4 TV channels growing up so I don't remember Sega of UKs marketing campaign back then