I think Russia has a chance with this to actually turn the tables on the west. The thing with migrations is while yes it can be tough to figure out how to handle all these people coming in all at once if you can get the infrastucture in place and get the economy growing fast enough so they all have jobs and just let them all come jt can be a MASSIVE boon to a region long term. Its part of why America grew so fast following colonization. If America hadnt had so many immigrants coming in they wouldnt have been able to have the economy they do today. These days America has shifted to an anti immigrant policy and i think its a huge mistake.
Russia has a lot of land. If they get Chinas help to pump out infrastucture and they start welcoming immigrants with open arms in 50-100 years Russia could be an economic powerhouse. And europe with its anti immigrant policies will be waning.
Its pretty simple. Workers create value. Immigrants coming means more workers which means more value. Let them come, create jobs for them to do, and you will prosper.