I can't speak for anyone else, but I am not aware of anyone saying that she should be in because of her skin tone. But it would be a good thing representation-wise.
That's the thing.
I'm not saying "hey put these characters in because of diversity", I'm saying "I personally love these characters and want them in Smash, and the added benefit of diversity comes with".
There's a difference. Broadly speaking, representation matters, whether it does to you personally or not. I have the Smash Switch bundle, I'm getting the Fighters Pass, whether Elma is confirmed or not is not a huge deal to me even though she is my most-wanted plausible next to Phoenix Wright. But to have a cool character who is the most important character of a major Nintendo Wii U release who
also is solid rep is only a good thing.
To use a non-Elma example, I'd be super happy if they made Doc Louis playable in a future game because he could be a trickier, heavier Little Mac, he's hilarious in the Wii Punch Out, and he's a fun recognizable character. It's also cool that he's a black man and all those factors combined would help him stand out and be a fun rep of a series I love.
It's really not that hard. I'm not gonna boycott a game over it, and I seriously doubt anyone is ACTUALLY doing that, people just like to stir ****. But does that mean the conversation is meaningless? No.