The percentage of "reliable slavs" which against official socialist rhetorik always were the main pillar of the Soviet Union would instantly drop well below 20 percent,while the chinese would be the vast majority of the new soviet population. Thats a bad idea.
ITTL:
"
Order of the Supreme Command of the Soviet Union on December 24, 1950, No. 500: Great Comrade Stalin has declared the following:
In our great War of Liberation to rescue the proletariat of China after the savage bourgeois-capitalist-tyrant assault, it has been discovered that over 85% of the population of China are bourgeois kulaks and prone to capitalist subversion! By withholding vital food from our brave Red Army, in this time of heavy winter, these kulaks have made clear their Fascist tendency!
This shameful fact has necessitated a new responsibility: a new and glorious dekulakization and collectivization campaign. First, measures were taken to redistribute vital resources to our troops in the liberation of December 1950. Second, the multitudes of bourgeois feudal Sino-Fascist enemies of the Soviet state must be re-educated and liberated by serving the Soviet state! The rehabilitative gulag system welcomes them into its open arms! Third, the private property held by the bourgeois of China is hence redistributed to the brave people of the Soviet Union!
Some stupid people at the home front believe that the annexation of such a large territory would be "imperialist". This is falsehood, and dangerous sedition, that will only help our enemies! The Soviet system of socialism in one country is the only way to fortify against the capitalist-fascist threat! And the only way to protect people of China from the capitalist-fascist threat, too, is to relocate their bourgeois to the productive centers of Siberia!
Comrade Joseph Stalin's ingenious plan ensures that this multitude cannot be turned against us, and will be used to further global socialism."