I'm fine with Link returning. As for Zelda, I'd definitely make her playable. The villain should be someone new. Maybe it goes like this:
Games starts off with Link going through a dungeon and taking down guards, etc...
Confronts Zelda and has a battle against her.
He wins but both are exhausted.
Villain appears, admits to Zelda he has been manipulating her in various ways to oppose Link.
Villain then corrupts Link, makes him his right hand man and banishes Zelda from Hyrule.
Bam, Zelda's quest to save Hyrule starts from there.