I think Vince Carter could make a great coach. He went from an athletic freak of nature to carving out a 20+ year career. You don't make it that long without a great understanding of the game. I also think he came up in a great time where he is relatable to the younger guys who watched him as they grew up, while he still has a grasp on the current layout of the NBA.
Another player I think would make a great coach, though he isn't playing technically, is Chris Bosh. He seemed to have a great grasp on the game and what a team needed to win.