This is a fascinating article published by the China Daily Mail, originally sourced from the NYT.
Why China will “reclaim” Siberia | China Daily Mail
The article speculates that China will one day use typical Russian policies to annex Siberia. Firstly, it would offer Chinese passports to Siberians and then it would annex Siberia to protect Chinese passport holders.
Personally, I find it rather far-fetched. But Siberia would be strategically attractive in terms of both mineral resources and massive space for the Chinese population.
Of course, with Western sanctions, Russia will not want to speculate on Chinese territorial expansion into Siberia. These days, with Russia dependent on mineral wealth, largely from Siberia, this would be a catastrophe scenerio for Russia.