Okay. A few things about this.
1. I fail to see how the roster isn't diverse already. I'm not being facetious about this either. We have dragons, mutants, robots, plants, magicians, anthropomorphic animals, children, regular animals, witches, angels, goddesses, gods, plumbers, and ninjas, just to name a few. They shoot fire, guns, lightning and water; wield swords, axes, and bows; are good, evil, or neutral in their moral alignment; and are female, male, or have no gender. Some of them are royalty and some of them had humble beginnings; some of them are extremely powerful and some of them are incredibly weak; some prefer to work in teams while others prefer to work alone. They are characters that are kind, cruel, dastardly, brave, courageous, independent, cowardly, silly, serious, strategic, clever, impatient, resourceful, beautiful, ugly, intelligent, stupid, disgusting, happy, violent, optimistic, rash, benevolent, peaceful, organized, hilarious, heroic, destructive, and hairy. If the reason you haven't purchased this game is because you can't identify with one of the 80+ characters, then I doubt you can identify with anyone or anything. This is a pretty diverse spectrum.
2. I find it incredibly hard to believe that anyone is waiting for a character with a certain arbitrary personality or character trait to join before they purchase the game. I'll go a step further and say that I doubt that adding a character with said trait(s) will cause someone to break into the fighting game genre, decide to be a Switch owner, or start playing video games that wasn't already before (or at least very much on the fence alresdy). It's not like a lesbian is somewhere just waiting for CNN to report Tracer was added to Smash, or a PoC is waiting for Kotaku to report that Twintelle was invited to the party. This premise is ridiculous. Will it appease some fans? Sure, I guess. But not as much as Geno, Doomguy, Crash or Lara Croft would.
3. If people are really this hung up on their very narrow ideas of what qualifies as "diversity", I recommend that they pull their head out of their ideologies and enjoy reality. There are so many interesting and exciting characters that are in Smash and gaming in general! These characters (their stories, worlds, abilities, personalities, franchises, and supporting actors) are so complex and interesting that it would be a real shame to miss out on that just because of their race, sexual orientation, gender, or some other criteria. Tracer, Cyrax, Kerrigan, Lara Croft, and Samus Aran are some of my favorite video game characters. I am a male, straight, and Caucasian. I am not allowed to like them because I don't identify with these arbitrary standards? Of course not! That's preposterous. And even if a character was chosen for a reason like this, fans would never be satisfied. These kind of people will always find something to be offended about. It will never be good enough.
TL;DR: I think adding characters for the sake of fulfilling someone's idea of diversity is ludicrous, unprofitable, and unnecessary. I guarantee it's not how Sakurai and Nintendo are choosing characters, so it best to abandon that thought process all together.