Like they did in the past, updating from Train Simulator 2015 to the upcoming 2016 will be free. BUT, when you buy TS 2016, you will get ‘exclusive’ and new content. And that will be precised later.
At least, they confirm there will be ‘extreme challenges’ included, to let you experience more or less difficult services with hard weather and time tables, or complex operations.
They are also working on the next generation of Train Sim that will take advantage of Unreal 4 game engine.