Skull Kid is one of my most wanted Zelda characters with Toon Zelda/Tetra a close second. I loved and hated Majora's Mask so Skull Kid has a tender place in my heart. That being said, I understand his chances are slim at best. He is a minor villain that had the best chance of appearing in Melee alongside Young Link. If that would have happened, may may have seen Zant in Brawl and liken the odds of Ghirahim for Smash 4. Additionally, the Majora's Mask version plays a fairly large and important role in MM but, outside of that, he fades into obscurity.
His only chances of being made playable is if MM receives a 3DS remake while during Smash 4's development time. Seeing how that's now and we have yet to receive any legit whisper of a remake, that is a moot point. As well, that is basing an argument entirely on a wistful speculation and can't be considered a legimitate point. If a MM remake is announced this year, I would say Skull Kids chances will fair much better.
Skull Kid is one of those few characters that, despite being from a major series, has little chances of being made a clone or semi-clone. As most, that could give him a Shiek moveset but that wouldn't fit him. He would be a unique character most likely.
However, he had the Demon Lord Ghirahim, Toon Link, Toon Zelda, Impa, Tetra, Tingle, Demise, and possible a new Wii U Zelda character to contend with. Each character is more recent than Skull Kid and, in terms of relevancy, is more likely.
Skull Kid is a very sad character. He could be a very interesting antagonist in a story mode. I can imagine him seeing all the other Nintendo characters "playing" and, due to over excitement, ends up dropping a ****ing angry moon on them.
Which brings me to the next point: Skull Kids Final Smash would be amazing in every way possible. The thought of that constipated moon dropping into the stage and causing massive damage makes me all happy inside.
Skull Kid would certainly be an interesting character with a 100% unqiue moveset involving fairies, flutes, evil magic, and a butt ugly moon. However, he lacks the relevancy and iconic power (not to say other Zelda character do though). Sadly, Skull Kid will be a no show unless a MM remake cones out and Sakurai becomes interested in the character.
For Skull Kid;
Wants:
4.80
Likelys:
1.32
Ghirahim's Prediction:
2.45
Noms:
M. Bison x2
Andy x2
Mach Rider x1