You should make an DLC in which we will have new tracks from this season like nurburgring and portimao. Also you could implement them in career mode by giving players the ability to choose which tracks do they want to race in that season. For example you have britain nurburgring and hungary and from those three tracks you pick two of them for the next season. That way you woudnt have to do much tweeks to a new calendar system implemented in this game.