I don’t know if that specific rumor will turn out to be true, but it sort of fits with this quote from Masahiro Sakurai.
“To me, it feels like the finish line is sliding farther away,” he said. “You may wonder, ‘How much longer can he be involved with Super Smash Bros. Ultimate ?’ But I’m also excited. Adding more characters into the game means more game worlds will be added to the series, and ultimately, that means there will be an even greater opportunity to delight the fans. At the same time, I feel that Super Smash Bros. Ultimate is representing so many characters and game worlds that it’s become an enormous game. Even if the Super Smash Bros. series continues moving forward, I doubt there will be an opportunity to bring this many characters together again, so I want to keep improving on this record as much as possible, and I will continue to work hard at developing the game. I appreciate your support.”
(from Polygon’s coverage of the direct)
Basically, “we’ll never get this many characters again, so let’s just go nuts”