There are no such things as a "rep" in the first place.
We don't play as reps, we play as playable characters.
Also, villain clamoring isn't a sole reason to rely on. Only gameplay and relevancy (as in they aren't some obscure character, like say Link's Uncle in ALTTP; not this "oh, this franchise doesn't matter" crap) matters, especially gameplay.
I don't see why Ghirahim would get in, because gameplay-wise he offers less than Midna (a more popular character) and Zant (a more popular character) from a more popular Zelda game, and yet, neither of them are playable.
Also, Demise, Impa, and Tetra trivialize Ghirahim with popularity and options (given that Tetra and Impa could both be Sheik clones, Demise could be a Ganondorf clone).
It also doesn't help that Ghirahim is the next Zant, who was the next Vatti, who was the next whatever the villains in OoA/OoS, who is the next Skull Kid, who was the next Aghanim, who is the next Dark Link.
I see your point, but Midna, Zant, Impa and Tetra could have made it into Brawl, and were put aside for characters like Wolf, who appeared in Star Fox: Assault only a couple of years earlier. I think contemporary relevancy is more of the key here for new characters (see: Greninja, Robin, Lucina) which is why characters like Shulk and Chrom had such strong bets to get in. Midna and Zant have only made a reappearance in Zelda because of Hyrule Warriors (Twilight Princess was released 7 and a half years ago), whereas Skyward Sword came out just under 3 years ago and this makes the characters fresher and more updated. If we saw the Bridge of Eldin stage in Smash 4, you could quite safely say that you expect a Twilight Princess character, but as of right now a Skyward Sword stage has been announced and that increases the potential for a character from that game.
The main discussion here, then, is between Impa, Demise and Ghirahim, the three most likely characters to be added (if one is to be put in). Sorry Groose, but impaling people on your hair is not allowed in Smash. Impa would almost definitely be a clone of Sheik, but I could actually see Impa working better as an alt. costume for Sheik, even if the names are different, but because Impa gets little-to-no action in Skyward Sword at all (save that one epic fight with Ghirahim) I can't see her being considered for a role. Demise is easily the most likely of the three to return, although I foresee Demise as an alt. skin for the inevitable Ganondorf and not a separate character in his own right, mostly because his screentime was so minimal in Skyward Sword that a lot of players may just think "who's that?".
Thus brings to me to Ghirahim, the antagonist for the majority of Skyward Sword who did effectively stand in for Ganon/Demise for the game. His playfulness, flamboyancy and cool design won him a lot of fans, arguably even more so than Zant in Twilight Princess (even though I absolutely love Zant), not to mention Skyward Sword's heavier emphasis on story than Twilight Princess, even if TP did lay down the narrative quite a lot, which solidified the character in people's memories permanently. In a popularity contest between Ghirahim and Zant, there would be quite a clear winner, I believe.
But Smash is not a popularity contest. Analysing how the two would likely fight in Smash, I think it's going to be quite clear that Ghirahim comes out on top. In Twilight Princess, Zant's frenzied attacks consisted only of two types - ranged purple orbs and wild sword attacks. His specials would probably involve a mix of the two, with a ranged attack for his neutral B, that crazy spin attack from the final fight as his side special, and maybe using one of his indisposable Zant heads to boost him up for his up B. Ghirahim, on the other hand, has more than one fight with Link and therefore displays more abilities which could be transferred into Smash, like using his quick teleport ability for recovery, his ranged pins as a side special, and a charged sword swipe as his neutral. In the game, his mobility is his biggest strength, so perhaps he could have a short range teleport attack like Metaknight's down-B.
Overally, Ghirahim is simply the most likely unique Zelda character to appear. I'll eat my hat if Groose makes it in, and I'd bet against a Twilight Princess character emerging, but outside of Demise there isn't much competition for Ghirahim.
EDIT: Yeah this should probably go in the Ghirahim thread lol.