Folks sure forget things quickly around here. The Cold war ended largely because people figured out that the major powers were going nowhere with enormous arsenals of nuclear weapons pointed at each other. Those aresenals still exist and those rules (it is suicide to strike a vital interest of a nuclear power) still exist.
To be very blunt, no China is not going to swipe Siberia from Russia.
If China ain't then I suppose no one will (except maybe the Islamacists who don't seem to need nukes).