The newly dubbed "Christmas Constitution" simplifies much of the NAC's government. The largest changes involve the creation of a diarchy, wherein Prime Minister Marx will be crowned as a junior monarch and ruling partner to Emperor William's senior crown. Emperor William will maintain his imperial rank and title, though they will have cultural significance rather than political. The dual monarchs shall be advised by an Imperial Cabinet.
The body that was the Senate shall be replaced with a Council of Junkers, similar in structure to Delvera's Council of Governors. This Council shall act as a mediating and balancing force to the Crown's legislative and executive powers, determining the constitutionality of actions taken by the Government.
You can see the complete "Christmas Constitution", including the Bill of Rights, here.
The new Constitution, including Prime Minister Marx's ascension to the Junior Crown, shall go into effect on the 25th of December, 2019.