If I was in charge of Smash and I didn't have an anti-Zelda bias like Sakurai then I would have completely revised Link and Zelda's movesets and Zelda would be in her BotW incarnation (the best one).
Link:
Neutral Special: Hero's Bow- Shoots his bow but now you can aim it. Used in the air, his falling speed drastically slows.
Side Special: Flurry Rush- Like his old final smash, Link dashes forward in a line and slashes and stuns the first enemy he contacts.
Down Special: Urbosa's Fury- A lot like Pikachu's thunder but instead of being centered on him directly, the lightning appears on both sides of him.
Up Special: Revali's Gale- Link whirls really high straight into the air. Vertical movement only.
While holding the jump button, Link pulls out his glider and sort of floats like Peach but faster and with more horizontal movement. Daruk's protection is his shield and his final smash is an ancient arrow. His normals all use his sword and shield. I don't know how you would do Mipha's Grace.
As for Zelda, I'm still working on her. But the gist is her moveset revolves entirely around the Sheikah slate since she's a scientist in the game. She would get bombs, magnesis, time-stop etc.