That's really difficult to speculate on now. The game has changed. The NX wont be as strong as the PS4Pro and Scorpio, so if anything it might be like the Wii. Whatever the NX gimmick is, if its successful, then I think Sony and MS might create an add-on like Move or Kinect for their current gen consoles. I think the earliest another 9th gen console comes out, is probably around 2018.