I have previously speculated that it will be Hyun Jin "Preston" Moon but there is some reason to believe that younger son arms dealer Kook-jin "Justin" Moon will take over the reins. One thing I know about the Moonies is that logic and reason have no place in the decision-making process--egomania and cupidity are the relevant factors. If nothing else, Kook-jin would be the apt choice because it is fitting that the Moonies are headed by someone with the word "kook" in his name.
For a list of my best posts on the Moon family and the Unification movement, click here.
Also, watch the YouTube video about Moon: The World's Most Powerful Cult