Ray Allen will one day be a head coach in the NBA. He's got all the earmarks. He's a consummate professional. He's got encyclopedic knowledge of the game. Players and coaches around the league respect him and respect what he's done. Most importantly, he strives for excellence and is driven to win, and expects the same from his teammates.
If he re-ups after next summer, the end of his next contract might then coincide with the end of the Big Three Era in Boston, at which time Doc Rivers may also think about changing career paths.
Giving Ray Allen a shot at replacing Doc wouldn't be the worst thing that Danny could do.