Described in full detail by this VGC article.
Sakurai says Ultimate is the ultimate (pun intended) collaboration in gaming, and that if there are more Smash Bros. games, then there's no way this many fighters, and series, can be represented again. There are still requests all over the world for new fighters.
He added that, as long as there's an opportunity to make more fighters, he wants push the record further.
So he's saying there very well might be more Smash Bros. games because of all the requests for new fighters, but not all fighters from previous games would come back in subsequent games?
I like that the opportunity for new Smash games is still there, but if not all of the previous games' fighters can come back, makes me appreciate Ultimate a lot more.
How do you feel about this?