I think Anthony taking over the family much like Michael did in the first part would be going over a complete circle. Michael was an improbable choice as well, if you see the scene after Don's shooting, everyone including Tessio, Clemenza and Sonny laugh at him for suggesting revenge. Similarly Anthony might be an Opera singer, but he could take over the Corleone family and eliminate his enemies. I would be most interested in seeing that plot for GF4.