Beyond Geno, I want this more than anything. Even if it's true that they choose most of the characters on relevancy, that doesn't mean it has to be all of them. I know people will point their fingers at certain communities and how vocal they can be about this character being deserving in the game or being better fits, but honestly the worst part of Smash speculation I've seen is the people who use the relevancy argument to shoot down characters and other people's hopes for the game. I've seen so many people use that line of thinking to beat down opinions of characters too many times at this point. Yes, several characters are not relevant to modern Nintendo or have limited appearances, or even limited fan bases.
So what? What does that matter in a game that is a celebration of all things Nintendo and gaming? Obscure characters deserve just as much light as main characters, and as long as Sakurai believes in their move set potential, he can realize any character. There's no such thing as a bad character for Smash if they're coming from Nintendo in my mind. Even third parties get a significant amount of leeway in that department even if I'm not completely willing to open the flood gates to third party characters quite yet, especially those that have less relations with Nintendo in the grand scheme of things.
Beyond that, what I perhaps hate most of these relevancy discussions is that it devalues all the work and effort Sakurai puts into these games. They act as if Smash is only an advertising machine for what is popular at Nintendo at the time, and that couldn't be further from the truth. From everything we've seen, Sakurai adores the game and puts his heart and soul into it. Even if corporate has made requests, he's worked so hard to bring us years of entertainment and deliver a product with soul that does call back to as much of the previous history in Nintendo he can. He brought attention to Ice Climbers, Mr. Game and Watch and R.O.B. Characters that no one had any idea about prior to Smash. I'd argue Earthbound's modern release and the localization of the original Mother come from his work in making a niche franchise recognizable. Fire Emblem owes everything to Smash, and the Kid Icarus revival owes everything to Smash and Sakurai. Irrelevant and strange characters have made it in to the game, and Smash is a second chances for characters and games to get recognition they might otherwise never see. In addition, everything about Ultimate points to Sakurai making the fans his number one goal of satisfying.
Beyond all of this, the trio I support of Ridley, King K. Rool, and Geno would be the validation of all characters in a way in they're all in. Ridley proves that no character is "too big" or doesn't fit Smash. King K. Rool proves that bigger names from the past can still make it in to Smash. Finally Geno proves that, yes, any one-off character can make it in to Smash, as long as they have a following and support. Smash speculation would be split absolutely open, and the relevancy argument would lose a lot of its clout. I know it's foolish to assign so much more additional meaning to Geno's inclusion, but I believe it at this point.