It seems on lost that being a Leader has always been a key theme, yet Richard has said "There can only be one at a time". Hmmm could this be because of Esau?
firstly let me say we only know about 4 leaders, Locke, Ben, Widmore and Ellie. Out of these only 1 has been killed the others (as far as we know) cannot be killed. Richard makes sure that Ellie cannot go into Dharama villie so she wont get killed. Could this be because Esau (not locke) requires a Leaders body to kill Jacob?
Now with Locke being dead and Richard not knowing perhaps Esau became the Leader?