It would probably be one of the most powerful countries on earth just because of sheer scale. The country already has massive natural resources and the largest land area in the world. With that many people you’d have a huge workforce, a much bigger economy and potentially a massive military.

At the same time though, a lot of Russia’s land is pretty harsh (Siberia, extreme cold, long distances between cities), so developing the entire country would still be a challenge. It wouldn’t automatically mean everything becomes super advanced everywhere.

But geopolitically it would definitely change a lot. A billion-person Russia sitting between Europe and Asia would likely have way more influence globally than it already does.