To be fair, who even knows what "semi-retired" would actually entail for Sakurai? The man has been known to work himself beyond typical human limits.
But, yeah, as Mondo has pointed out, it appears the "semi-retired" comment might not be the most useful to go on, with stronger nuance in the conversation.
he also talks about how he was motivated by Smash wrapping up & realising his time as a working dev is limited—he's 52 now & he'd been working on Smash for 9 years straight; games take so long to make nowadays that if he kept working on them with the same commitment, his life...
...would be eaten up in a blink, and there's no guarantee he'll have the option of relaxing later, either, so the video channel is him doing it ASAP while he still has time the channel's not a forever thing, either: it will eventually end, hopefully with a bang
No comment he makes precludes him from directing or working on another video game again, just that he doesn't want making games to be the only thing he does for the remainder of his life.
Can't say I blame him there, really. He might be especially passionate about the industry and medium, but that doesn't mean he can't have other things he wants to do, and he's even in a position where he can make those choices.
I could see the next Smash release indeed being Smash Ultimate Deluxe of some sort, where someone else handles new content (same basic game but a handful of new characters, stages, some new modes and MAYBE new single player campaign or so), with Sakurai just keeping an eye on it.
It does create a situation where this becomes a distinct
possibility, whatever such a project ends up being in the end. As someone looking at development times, the past nine years of
Smash Bros. production, the future and his current point in life, as well as a desire for his remaining time to not be consumed entirely by the game development, it's possible he might seek to train curators for the future, rather than take on the full responsibility.
And, given all that, it's worth noting he doesn't even have to come back for further entries (despite the guaranteed paycheck); he can absolutely decline, though I suspect he'd want to ensure it's in good hands going forward.
Yeah, I could see him taking a more hands-off approach, which could theoretically lead to ah something more akin to a
Super Smash Bros. Ultimate Super release -- again, whatever that might end up being in the end.
Alternatively, he might want to see what prospective replacements might create from scratch, but that could also be more intensive overall, though at a smaller scale.