He had his day and yes he can still hang a bit but why not let some new young guys work into davis cup and help them become better players. I don't think he should be competing with his players on the team as his title is now coach. My youngest daughter is 4 years old and already swings a racquet on a regular basis. If they want to play then keep working with them. I think the biggest mistake is to force them to play.
Kids have to want it themselves.
It is just like any other tournament. Single elimination with a playoff for third and fourth for the bronze. Talk about the emotion of playing Davis Cup. Davis cup is the most exciting event of my career. It was heartbreaking to lose in the 5th but exhilarating to win the tie.