I want Tetra to be in as a lightweight Sheik clone, and pull out her dagger for a taunt.
Seriously though, I'm tempted to say that Tetra has the highest chance as a Zelda DLC character, but I'm honestly not sure. There's never really been one Zelda character that stuck out with the community as the one character that everyone said "Oh yeah, that's gonna be Zelda newcomer."
That strikes me as odd, because almost every other already-in-smash series had that.
- Mario had Bowser Jr.
- Pokémon had Mewtwo (who also represented the idea of having am XY Pokémon, which we got in Greninja)
- Fire Emblem had Chrom and Robin (who the community was split between, with most leaning to Chrom because of the Gematsu Leak)
- Kid Icarus has Palutena
Even series that didn't get a newcomer at launch date have the ideal DLC newcomer in the eyes of the community.
- Donkey Kong Country has K. Rool and Dixie Kong (community is split)
- Kirby has Bandana Dee
- F-Zero has Samurai Goroh and Black Shadow (community is split)
- StarFox has Krystal
But Zelda doesn't have that one character that sticks out as the ideal newcomer, the closest thing we had was Ghirahim, but even then he was a one-shot villain.
There are several characters that could be newcomers, like Impa, Tetra, Vaati, and Classic Pig Ganon, but none really stick out above the others.
Maybe it's because Zelda has all of its main characters, and anything else would just be a side character who is pretty unimportant in the long run.