The only way to read this is that John Roberts has become so upset by the radicalism of his court that he's asking the current president to assassinate all the justices that agree that doing so is legal. It would almost be rude not to.
The president is himself forever immune from prosecution for crimes committed using his official power, and he can pardon anyone for helping him to commit federal crimes, explicitly including an actions in furtherance of a coup to illegally hold onto the office of the presidency. That’s the upshot.
