Pretty sure he said something similar after the last one

Honestly, he has tried to perfect what he built each generation and, hopefully, we will get to a point where it is balanced and we just need new levels/new characters, and visual upgrades and really nothing else for generations to come. He has done like 90% of the groundwork for pretty much every future Smash game, so it's probably ok to let someone else do the remaining 10%.

Honestly at this point he isn't needed. He has gotten the game to a point were minor additions will be enough for the next two games. In that time someone can learn the ins and outs of the game and then when they make a third it be the next step up.

The next two future versions all they need is beefed up visuals, higher res, new chars and new maps.

Third-party characters will be a lot harder to get without Sakurai. People seem to underestimate how highly respected he is in Japan. Square-Enix probably never would have allowed Cloud if not for it being Sakurai who was asking.

It's called Ultimate. So there better not be another one or they're a bunch of liars!

Click bait article from Nintendolife. Will it be his last? Probably but Smash will continue on.

Hasn't he said it would be the last the last few times? 

Fool me once....  Shame on.... you...  Fool me twice... Can't get fooled again.  Hehehe  - Bush Jr.

The Switch should last for a long time.

Super Smash Bros. INFINITE 

Let the man die in peace