Yeah, in Seven Sirens at least you can see the outline of her legs through the fabric, but that's about it. Dunno how well that would translate to 3D while keeping that age rating intact though.
To not skirt the rules as much, I'll follow up on that moveset comment, because I do wonder how Shantae's moveset would go. The hair-whipping would have to make up a decent amount of her attacks, but I wonder if there's room for some hand-to-hand moves here and there. I think the first game unlocked a couple combos, though I haven't played any of them so I can't say for sure. I also know Pirate's Curse in particular gave her a sizeable arsenal of gear, but they're all swiped from Risky Boots and are given back by the next game, so I dunno how well that would work for Smash's sake.