You can personally decide about the World Wars part. And a lot. Also, are the Gastarbeiters actually going to bea llowed to permanently stay in Russia and to eventually acquire Russian citizenship for themselves and/or their descendants?
Ok, let us have a PoD where stuff mostly goes well for Russia in the 20th century, no Russo-Japanese war, and Russia and Japan find a way to live together, instead.
Russia somehow ditches the Serbs, possibly siding with the Bulgarians on a few issues and letting Bulgaria and Austria-Hungary split up Serbia, hence no Black Hand.
Obviously no world wars, or there are some European general wars in which Russia and its European proxies stay neutral.
That IMHO will give Russia's population a significant boost, this will also require land reform and more capitalism.
Frankly, if technology develops as it did in OTL and the deaths and forced migrations of the various wars are gone away with Russia can probably have 3x the population and industrialize about as fast as it did in the OTL, they will need to develop Siberia, and if they keep their gains from China those areas can flourish as well, and attract Chinese and Korean settlers in the process.
At present there are around
400,000–550,000 Chinese in Russia and just as many
Koryo-saram scattered across the former USSR.
TBH that can go up 5-15 times, given Russia is stable and stuff goes about as bad as it did for the rest of Asia in the OTL.
We'd probably see a lot more Mongolians moving into Russia and Mongolia, too.