It already happened in Majora's Mask, Wind Waker, and Phantom Hourglass. In MM, you switch between Link and Kafei in the theif's hideout. In WW, you switch between Link and either Makar or Medli. They don't fight but they help with puzzles. In PH, you switch between Link and a goron who can fight. He crushes opponents as a ball and fights the first phase of a boss.