I still think Tetra has a pretty good shot. I find her to be more likely than most Zelda candidates. She can easily out represent most of the Zelda characters that people are thinking have better chances. She has been in three different Zelda games, plus a remake that makes her way more relevant now than other Zelda characters. I'm not here to discuss relevancy though, as I don't truly believe that a character's relevancy is what merits them to take a slot on the roster. An argument that most people go to when discussing Ghirahim's chances. I believe that a character has to be able to represent their franchise well enough to even be considered. Tetra can do that as she is a child version of Zelda. Most of Zelda's incarnations have been a child after all. On top of that, she can bring in a unique move set just like Sheik did, but still be completely different than her counterparts. The only other character that you mentioned that I think would be a better choice to represent the Zelda franchise is Ganon. I don't see him happening at this point though because I think they would have already revealed Ganondorf by now if Ganon was on the roster, and Ganondorf already has Ganon as his Final Smash; something that I don't think is going to change.
I never understood why people will say that Zelda, the title character of one of the most important franchises to gaming, can't possibly have three completely different variations of herself on the Smash roster. Always seemed like a moot point to me. A way to justify a character not happening over other potential representatives, but ultimately grasping for straws at the same time. We almost had four different Zeldas in Brawl. I think three can happen, especially if all three bring something completely unique to Smash while representing three big sides of the Zelda franchise. The adult magic user, the ninja alter ego, and the child pirate alter ego. All very different incarnations of a single character, and they even have different names. I just can't comprehend why people think that wouldn't be very good representation to the Zelda franchise as a whole. Different minds though.