Possible hints that Hilda is set to be an echo fighter of Zelda.
Hint # 1: Zelda's design in general - The first hint is just the fact that Sakurai chose A Link Between Worlds for Zelda's new design.
Hint #2: No Hilda Colors - The second hint is that, despite being inspired by her ALBW interpretation, Zelda does not have a color palette that references Hilda.
Hint #3: Zelda's new Kirby Hat - The third hint is that Kirby's Zelda hat is no longer Young Zelda's hat, but Zelda's hair, despite his Link hat still being Link's cap. This could possibly be to avoid confusion because there is no Young Hilda, so it would make more sense for the Zelda and Hilda hats to just be their hair.
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Hint #4: Zelda's new personality - Part of why Zelda's flashy and energetic personality is so emphasized could be to contrast it with Hilda's completely opposite personality.
Hint #5: Zelda's new Final Smash - Zelda's new Final Smash (The Triforce of Wisdom) could partly have been chosen to better suit a Final Smash for Hilda, which would most likely be an upside down triforce of wisdom. It's also possible that Sheik's new Final Smash was made to better fit Impa.
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Just like the theories about Shadow and Dark Samus, all of this could mean absolutely nothing, but I think Hilda would make a lot of sense as an echo fighter, especially with Zelda's new design. I believe Hilda and Impa are going to be echoes and this will leave Super Mario, The Legend of Zelda, and Pokemon with an equal amount of characters on the character select screen (8 with the addition of a Gen 7 Pokemon), which has been a series tradition with the past three games, with the exception of Super Mario having more in Melee and Smash 4.