I doubt it'll ever happen. Childress took the offer because he was a sixth-man in the NBA. Over there, he'll be a starter and making shit loads... makes sense for him.
LeBron going over there doesn't make sense. He makes millions upon millions on endorsements alone, his contract money is really like extra cash for him. With that said, I can't see him leaving to play for a Greek team when he's still yet to win an NBA championship. This is LeBron James we are talking about... the best player in the league. He's not going anywhere.