I think you could probably make the case that China, in their own ruthless and meat-grindery way, does try to foster a race + geographically diverse labor pool

I think you could probably make the case that China, in their own ruthless and meat-grindery way, does try to foster a race + geographically diverse labor pool by normalizing minorities into the Han workforce by whatever means necessary (exterminating local languages, exterminating religions, sterilizing women so they can join the labor force, etc). I don't think it's even remotely ethical, but from their perspective they are actually making strides on that front.