In the United States, the charge of treason only has meaning within the context of a declared war (due to it's specific definition within the constitution). Given that wars are no longer declared, I don't foresee even literal traitors being charged with treason until either a law is passed creating a different charge with different criteria, or Congress decides to check the Executive regarding the declaration of war. No reason to believe either are on the horizon; it's entirely possible no one will ever be charged with treason in the United States ever again.