Nintendo's actually already got quite a big shelf presence is stores like Toys R Us... it's a shame that they're all in the boy-centric aisle. And that's their problem. Their games may be gender neutral, but their marketing in America at least caters 80% to boys and 20% to girls with Animal Crossing and Tomodachi Life being exceptions. Even all the Mario toys and merchandising are found in the boy's section. You could've fooled me when you say Rosalina is popular. I haven't seen ANY merchandising with her in it.
Nintendo's games this year have done a fine job of showcasing their array of female characters with Tropical Freeze, Captain Toad, Bayonetta, Mario Kart 8, and Smash 4. But the marketing here in North America has failed to showcase that especially with Smash. Between both Smash versions, only one 3DS commercial actually showcased Zelda, ZSS, Rosalina, Sheik, Wii Fit Trainer, Palutena, and Peach in gameplay reels... and that was a commercial used worldwide. Every other commercial just shows Samus and the actresses using Kirby and Pikachu. Just from the commercials, girls would never know that the roster compromises of more than just dudes. Little girls aren't going to settle for a game playing as the Olaf when they really want to be an Anna or Elsa.
TL;DR: light a fire for under their North American marketing team's ass and tell them that they're overestimating how gender neutral Mario/Yoshi/Toads are. People want to be Peach/Rosalina/Zelda. They want to see that Samus is a woman. They didn't know that there's over 10 playable female characters in Smash 4. How could they? None of the North American Wii U commercials showed any of them besides armored Samus. Girls go to Disneyland to take a picture of Mickey. But their first priority in the day? Taking a picture with mother fuckin' Ariel, Elsa, and Cinderella.