China already has quite a lot of that within its own borders, though. If you look at a population map of China, the east coast is extremely densely populated, but the rest is quite empty.
EDIT: Not quite as I thought (though note the logarithmic scale) - the logical point of expansion in some directions will go into Mongolia relatively soon before it goes into western China - but then we might also compare the US, which had a similar map in the early-mid 19th century and (as far as I know) never showed any interest in annexing Nova Scotia.

EDIT: Not quite as I thought (though note the logarithmic scale) - the logical point of expansion in some directions will go into Mongolia relatively soon before it goes into western China - but then we might also compare the US, which had a similar map in the early-mid 19th century and (as far as I know) never showed any interest in annexing Nova Scotia.