While Krystal can be a touchy subject, I for one am against her inclusion barring we get a sufficient amount of popular characters. This pool (at least for me) includes Ridley, Mewtwo, Palutena, K.Rool, my favorite in Shulk, etc...
If we're going by series balance, then Star Fox as a series should not get a character in my opinion. This is the same reasoning I give F-Zero crap as well as Mother. None of those series got any sort of new content during the Wii generation. Star Fox has Command and then a remake of a game that Krystal didn't even appear in.
Mario makes sense to have 5. Zelda makes sense to have 5. Pokémon makes sense to have the characters they have... I thought 3 Star Fox characters was even pushing it, not even talking about 4.
If I'm being honest I would be far more interested in seeing Palutena getting in as a staff user. She's from a series with less representation. This is simply if we're comparing the potential movesets between Palutena and Krystal. I haven't played Adventures to know exactly what it does.
My beef with Krystal is that she has hardly had enough time to create a presence for herself between Brawl and now. Brawl would have been the prime time to add her because that is when she was in her prime. Similar to a sport, in which a team would trade a player who is reaching the peak of his skill to better themselves as a whole.
In my opinion, there are several other characters who would make a lot more sense to add than her. Star Fox is a franchise that I wouldn't call dead necessarily, but maybe...unimportant as of late. However, this doesn't really matter. It's up to Krystal herself to draw Sakurai's eye.
She used the staff in one game, and yes maybe she has psychic powers. But the rest of her appearances have her doing exactly what the rest of the crew does. Piloting a ship, and shooting things. So if Sakurai gave her a moveset entirely consisting of the staff, that would not be an entirely accurate description of her overall appearances as a character.
I'm not saying he has to be specific down to the last detail, but he looks for source material where he can find it, and overall, besides one game, she isn't all that different from the rest of them.
Also this whole notion of "reps" doesn't exist. Quit using that word.