Comment by tonytran2015: China has no valid claim to Siberia which has once been ruled by Mongolia who has also once ruled China. Should Japan take back China since Japan had once ruled China? (Understanding China’s Perpetual Wars against its neighbours, posted 2017 April 01.).
Now, a Beijing publication, Sohu, has done just that, saying that Russia faces some of the same problems the USSR did in 1991, will therefor disintegrate, and that this time around its neighbors, including China, need to be ready to seize the parts that used to belong to them (see in Chinese at sohu.com or in Russian at inosmi.ru).