

Are you kidding? China has always wanted the eastern part of Russia. Also, China not wanting it would apply to Russia too, right? If it’s worthless, why is anyone claiming it? It obviously isn’t worthless. At minimum, control of the coast and rivers are valuable. There’s also tons of natural resources there.
It’s a lot easier just to buy what they want, specially now when Russia doesn’t really have an option but to sell. It’s also politically much, much more easier than actually moving borders.
That is buying what they want. And moving borders isn’t that hard. They just need to reach an agreement. It’s not like they have physically go and move some line. Borders don’t exist in reality. It’s just what states agree to say they control. The biggest issue would be going in and collecting taxes and whatnot. China’s got the beurocratic infrastructure to handle that pretty easily though, and it’s not like there’s many people or much wealth (in the people) there anyway. It’s all about the resources. Like you said, they’ve been doing it in Africa. Why wouldn’t they do it in their backyard?

What do you mean he won’t allow it? If it’s literally selling it off for military aid, which is something he critically needs, that seems exactly like something he’d do.
I don’t see many people moving into Siberia no matter who owns it though. Few people live there, and few want to. It’ll mostly be for control of waterways and resources, but also for strategic control to push Russia away from its more critical locations.