I dont favour an FA/UEFA/FIFA ban for the likes of Hughes, McCormick or King. Besides, its illegal, you cannot under European Law deny a person their right to ply their legitimate trade.
Its down to the morality of individual clubs to decide if they want to pay huge sums of money to players like this. And hopefully, pressure from the decent elements of the fan base will mean not many clubs will step forward and their options will be limited.
One thing though : I cant see King demanding 35 grand a week and wearing Rolex watches when does find a club to take him after his sentence. He has seriously damaged his value. I suppose we will see how much he really wants to play football then...