How small would any Chinese Soviet Socialist Republic have to be to be a member of the USSR? And how much smaller would any Chinese Autonomous Republic have to be to be a part of the RSFSR?
Considering Mongolia, with all its closeness to the USSR (its nominally sovereign president was purged during the Great Purge for example), was not formally incorporated into the USSR, how early of a POD would we need for any part of China to enter the USSR under that name?