I don't know about that.
The guy knows how to lead. He absolutely kept ALL his players in check on offense. On leadership aspect alone I firmly believe he could outcoach Wanny right now.
X's and O's aspect of the game. It wasn't just Marino's arm that made him great. He was known to be one of the best at reading a defenses coverage scheme and was able to do it in a millisecond! I think it's fair to say he could develop a gameplan to take advantage of an opposing defense.
I think Marino does have the basic tools to become a good coach.
2 Reasons it will never happen.....
1) First off, You just don't start out as a HC. So Marino would never be offered the HC job for the Phins in 2005. He'd have to start as a position coach and work his way up the ranks. Your talking about years of commitment and learning.
What's his motivation? Marino just stepped down from a FO position because he did'nt want to give up time with his family.
2) Marino has a great job in broadcasting.
A job that allows him to still be attatched to the game of football while being able to have all the time he needs to see his kids grow up.