I would love the hipster Bowser wearing glasses from some early 3DS commercials in Japan. But it's unlikely to happen. Also, a Dry Bowser costume would have been cool.
Dry bowser would be neat. Ganondorf NEEDS a Phantom Ganon outfit from Oot. Inkling needs an Octoling skin. Pokemon Trainer needs Trainer Red and Trainer Blue skins. Luigi needs a Mr. L suit. Link needs his TP suit back, and maybe a better Fierce Deity Suit that doesn't look like its 3 sizes too small.